MARVELS OF POND-LIFE
OR,
A YEAR'S MICROSCOPIC RECREATIONS
AMONG THE
POLYPS, INFUSORIA, ROTIFERS, WATER-BEARS,
AND POLYZOA.
BY
HENRY J. SLACK, F.G.S.,
SECRETARY TO THE ROYAL MICROSCOPICAL SOCIETY;
AUTHOR OF
'THE PHILOSOPHY OF PROGRESS IN HUMAN AFFAIRS,' ETC. ETC.
SECOND EDITION.
ILLUSTRATED WITH COLOURED PLATES AND NUMEROUS WOOD ENGRAVINGS.
LONDON:
GROOMBRIDGE AND SONS,
5, PATERNOSTER ROW.
MDCCCLXXI.
PRINTED BY J. E. ADLARD,
BARTHOLOMEW CLOSE.
INTRODUCTION.
As this little book is intended to be no more than an introduction to an agreeable branch of microscopical study, it is to be hoped it will not require a formal preface; but a few words may be convenient to indicate its scope and purpose.
The common experience of all microscopists confirms the assertion made by Dr. Goring, that the most fascinating objects are living creatures of sufficient dimensions to be easily understood with moderate magnification; and in no way can objects of this description be so readily obtained, as by devoting an occasional hour to the examination of the little ponds which are accessible from almost any situation. A complete volume of pond lore would not only be a bulky book—much bigger than the aldermanic tomes which it is the fashion to call "Manuals," although the great stone fists in the British Museum would be required to grasp them comfortably,—but its composition would overtask all the philosophers of our day. In good truth, a tea-spoonful of water from a prolific locality often contains a variety of living forms, every one of which demands a profound and patient study, if we would know but a few things concerning it.
To man, then, is a vast and a minute. Our minds ache at the contemplation of astronomical immensities, and we are apt to see the boundless only in prodigious masses, countless numbers, and immeasurable spaces. The Creative Mind knows no such limitations; and the microscope shows us that, whether the field of nature's operation be what to our apprehension is great or small, there is no limit to the exhibition of marvellous skill. If the "undevout astronomer" be "mad," the undevout microscopist must be still more so, for if the matter be judged by human sense, the skill is greater as the operation is more minute; and not the sun itself, nor the central orb round which he revolves, with all his attendant worlds, can furnish sublimer objects of contemplation, than the miraculous assemblage of forces which make up the life of the smallest creature that the microscope reveals.
There is an irresistible charm in the effort to trace beginnings in nature. We know that we can never succeed; that each discovery, which conducts back towards some elementary law or principle, only indicates how much still lies behind it: but the geologist nevertheless loves to search out the first or oldest traces of life upon our globe; and so the microscopist delights to view the simplest exhibitions of structures and faculties, which reach their completion in the frame and mind of man. That one great plan runs through the whole universe is now an universally accepted truth, and when applied to physiology and natural history, it leads to most important results.
The researches of recent philosophers have shown us that nature cannot be understood by studying the parts of animals with reference merely to their utility in the economy of the creature to which they belong. We do, indeed, find an admirable correspondence between structures and the services they perform; but every object in creation, and every part of it, is in harmonious relation to some grand design, and exhibits a conformity to some general mode of operation, or some general disposition and direction of forces, which secures the existence of the individual or the species, and at the same time works out the most majestic schemes. Microscopic researches, such as are within the reach of millions, offer many of the most beautiful illustrations of these truths; and although the following pages are confined to such objects as are easily obtainable from ponds, and relate almost exclusively to the Infusoria, the Rotifers, the Polyps, and the Polyzoa, it is hoped that they will assist in associating a few of the highly suggestive reasonings of science, with one of the most pleasurable recreations that human ingenuity has devised.
After a preliminary chapter, which is intended to assist the young microscopist in some technical matters, that could not be conveniently introduced into the text, the observations are distributed in chapters, corresponding with the twelve calendar months. This arrangement was suggested by the author's diary of operations for the year 1860, and although it by no means follows that the months in which particular creatures were then discovered, will be those in which they will be most readily found in other years, it was thought advantageous to give a real account of an actual period of microscopic work, and also that the plan would facilitate a departure from the dry manner of a technical treatise. The index will enable any one to use the book for the purpose of reference, and it will be observed that the first chapter in which any member of a group of creatures is introduced, is that in which a general description of the class is given. The illustrations are taken from drawings made by the wife of the author from the actual objects, with the exception of a few instances, in which the authority is acknowledged. The sketches were made especially for beginners, and the rule followed, was not to introduce any details that could not be seen at one focus, and with the simplest means: more elaborate representations, though of the highest value to advanced students, are bewildering at the commencement.
The ponds referred to are all either close to, or within a moderate distance of, London;[1] but similar objects will in all probability be obtained from any ponds similarly situated, and the descriptions and directions given for the capture of the minute prey will be found generally applicable. Care has been taken throughout to explain the most convenient methods of examining the objects, and although verbal descriptions are poor substitutes for the teachings of experience, it is hoped that those here given will remove some difficulties from a pursuit that no intelligent person can enter upon without pleasure, or consent to abandon when its elementary difficulties have been mastered, and the boundless fields of discovery are opened to view. Let not the novice be startled at the word "discovery." It is true that few are likely to arrive at new principles or facts which will inscribe their names upon the roll of fame; but no one of ordinary powers can look at living objects with any considerable perseverance, without seeing much that has never been recorded, and which is nevertheless worthy of note; and when the mind, by its own exertions, first arrives at a knowledge of new truth, an emotion is felt akin to that which more than recompenses the profoundest philosopher for all his toil.
[1] Many are now (1871) destroyed by the progress of building.
CONTENTS.
CHAPTER I.
MICROSCOPES AND THEIR MANAGEMENT.
PAGE
Powers that are most serviceable—Estimated by Focal length—Length of Body of Microscope and its Effects—Popular Errors about Great Magnification—Modes of Stating Magnifying Power—use of an "Erector"—Power of various Objectives with different Eye-pieces—Examination of Surface Markings—Methods of Illumination—Direct and Oblique Light—Stage Aperture—Dark-ground Illumination—Mode of Softening Light—Microscope Lamps—Care of the Eyes[1]
CHAPTER II.
JANUARY.
Visit to the Ponds—Confervæ—Spirogyra quinina—Vorticella—Common Rotifer—Three Divisions of Infusoria—Phytozoa—Protozoa—Rotifera—Tardigrada—Meaning of these Terms—Euglenæ—Distinction between Animals and Vegetables—Description of Vorticellæ—Dark-ground Illumination—Modes of producing it—The Nucleus of the Vorticella—Methods of Reproduction—Ciliated Protozoa—Wheel-bearers or Rotifers—Their Structure—The Common Rotifer—The young Rotifer seen inside the old one—an Internal Nursery—"Differentiation" and "Specialization"—Bisexuality of Rotifers—Their Zoological Position—Diversities in their Appearance—Structure of their Gizzard—Description of Rotifers[10]
CHAPTER III.
FEBRUARY.
Visit to Hampstead—Small ponds—Water-Fleas—Water-Beetle—Snails—Polyps—Hydra viridis—The Dipping-tube—A Glass Cell—The Hydra and its Prey—Chydorus Sphæricus and Canthocamptus, or Friends and their Escapes—Cothurnia—Polyp Buds—Catching Polyps—Mode of Viewing Them—Structure of Polyps—Sarcode—Polyps Stimulated by Light—Are they Conscious?—Tentacles and Poison Threads—Paramecium—Trachelius—Motions of Animalcules, whether Automatic or directed by a Will—Their Restless Character[30]
CHAPTER IV.
MARCH.
Paramecia—Effects of Sunlight—Pterodina patina—Curious Tail—Use of a Compressorium—Internal Structure of Pterodina—Metopidia—Trichodina pediculus—Cothurnia—Salpina—Its Three-sided Box—Protrusion of its Gizzard Mouth[43]
CHAPTER V.
APRIL.
The Beautiful Floscule—Mode of Seeking for Tubicolar Rotifers—Mode of Illuminating the Floscule—Difficulty of seeing the Transparent Tube—Protrusion of Long Hairs—Lobes—Gizzard—Hairy Lobes of Floscule not Rotatory Organs—Glass Troughs—Their Construction and Use—Movement of Globules in Lobes of Floscule—Chætonotus larus—Its mode of Swimming—Coleps hirtus—Devourer of Dead Entomostraca—Dead Rotifer and Vibriones—Theories of Fermentation and Putrefaction—Euplotes and Stylonichia—Fecundity of Stylonichia[54]
CHAPTER VI.
MAY.
Floscularia cornuta—Euchlanis triquetra—Melicerta ringens—Its Powers as Brickmaker, Architect, and Mason—Mode of Viewing the Melicerta—Use of Glass Cell—Habits of Melicerta—Curious Attitudes—Leave their Tubes at Death—Carchesium—Epistylis—Their Elegant Tree Forms—A Parasytic Epistylis like the "Old Man of the Sea"—Halteria and its Leaps—Aspidisca lynceus[69]
CHAPTER VII.
JUNE AND JULY.
Lindia torulosa—Œcistes crystallinus—A Professor of Deportment on Stilts—Philodina—Changes of Form and Habits—Structure of Gizzard in Philodina Family—Mr. Gosse's Description—Motions of Rotifers—Indications of a Will—Remarks on the Motions of Lower Creatures—Various Theories—Possibility of Reason—Reflex Actions—Brain of Insects—Consensual Actions—Applications of Physiological Reasoning to the Movements of Rotifers and Animalcules[76]
CHAPTER VIII.
AUGUST.
Mud Coloured by Worms—Their Retreat at Alarm—A Country Duck-Pond—Contents of its Scum—Cryptomonads—Their Means of Locomotion—A Triarthra (Three-limbed Rotifer)—The Brachion or Pitcher Rotifer—Its Striking Form—Enormous Gizzard—Ciliary Motion inside this Creature—Large Eye and Brain—Powerful Tail—Its Functions—Eggs[86]
CHAPTER IX.
SEPTEMBER.
Microscopic Value of Little Pools—Curious Facts in Appearance and Disappearance of Animalcules and Rotifers—Mode of Preserving them in a Glass Jar—Fragments of Melicerta Tube—Peculiar Shape of Pellets—Amphileptus—Scaridium longicaudum—A Long-tailed Rotifer—Stephanoceros Eichornii—A Splendid Rotifer—Its Gelatinous Bottle—Its Crown of Tentacles—Retreats on Alarm—Illumination Requisite to see its Beauties—Its Greediness—Richly-coloured Food—Nervous Ganglia[97]
CHAPTER X.
OCTOBER.
Stentors and Stephanoceri—Description of Stentors—Mode of viewing them—Their Abundance—Social Habits—Solitary Stentors living in Gelatinous Caves—Propagation by Divers Modes—Cephalosiphon limnias—A Group of Vaginicolæ—Changes of Shape—A Bubble-blowing Vorticella[107]
CHAPTER XI.
NOVEMBER.
Characteristics of the Polyzoa—Details of Structure according to Allman—Plumatella repens—Its Great Beauty under proper Illumination—Its Tentacles and their Cilia—The Mouth and its Guard or Epistome—Intestinal Tube—How it swallowed a Rotifer, and what happened—Curiosities of Digestion—Are the Tentacles capable of Stinging?—Resting Eggs, or "Statoblasts"—Tube of Plumatella—Its Muscular Fibres—Physiological Importance of their Structure[118]
CHAPTER XII.
DECEMBER.
Microscopic Hunting in Winter—Water-Bears, or Tardigrada—Their Comical Behaviour—Mode of viewing them—Singular Gizzard—Wenham's Compressorium—Achromatic Condenser—Mouth of the Water-Bear—Water-Bears' Exposure to Heat—Soluble Albumen—Physiological and Chemical Reasons why they are not killed by Heating or Drying—The Trachelius ovum—Mode of Swimming—Method of Viewing—By Dark-ground Illumination—Curious Digestive Tube with Branches—Multiplication by Division—Change of Form immediately following this Process—subsequent Appearances[128]
CHAPTER XIII.
Conclusion.—Remarks on Classification, &c.[140]
CHAPTER I.
PLAIN HINTS ON MICROSCOPES AND THEIR MANAGEMENT.
Powers that are most serviceable—Estimated by focal length—Length of body of microscope and its effects—Popular errors about great magnification—Modes of stating magnified power—Use of an "Erector"—Power of various objectives with different eye-pieces—Examination of surface markings—Methods of illumination—Direct and oblique light—Stage aperture—Dark ground illumination—Mode of softening light—Microscope lamps—Care of the eyes.
HE microscope is rapidly becoming the companion of every intelligent family that can afford its purchase, and, thanks to the skill of our opticians, instruments which can be made to answer the majority of purposes may be purchased for three or four guineas, while even those whose price is counted in shillings are by no means to be despised. The most eminent English makers, Wales, and Tolles, in America, and Hartnack, in Paris, occupy the first rank, while the average productions of respectable houses exhibit so high a degree of excellence as to make comparisons invidious. We shall not, therefore, indulge in the praises of particular firms, but simply recommend any reader entering upon microscopic study to procure an achromatic instrument, if it can be afforded, and having at least two powers, one with a focus of an inch or two thirds of an inch, and the other of half or a quarter. Cheap microscopes have usually only one eye-piece, those of a better class have two, and the best are furnished with three, or even more.
The magnifying power of a compound microscope depends upon the focal length of the object-glass (or glass nearest the object), upon the length of the tube, and the power of the eye-piece. With regard to object-glasses, those of shortest focal length have the highest powers, and the longest eye-pieces have the lowest powers. The body of a microscope, or principal tube of which it is composed, is, in the best instruments, about nine inches long, and a draw tube, capable of being extended six inches more, is frequently useful. From simple optical principles, the longer the tube the higher the power obtained with the same object-glass; but only object-glasses of very perfect construction will bear the enlargement of their own imperfections, which results from the use of long tubes; and consequently for cheap instruments the opticians often limit the length of the tube, to suit the capacity of the object-glasses they can afford to give for the money. Such microscopes may be good enough for the generality of purposes, but they do not, with glasses of given focal length, afford the same magnifying power as is done by instruments of better construction. The best and most expensive glasses will not only bear long tubes, but also eye-pieces of high power, without any practical diminution of the accuracy of their operation, and this is a great convenience in natural history investigations. To obtain it, however, requires such perfection of workmanship as to be incompatible with cheapness. An experienced operator will not be satisfied without having an object-glass at least as high as a quarter, that will bear a deep eye-piece, but beginners are seldom successful with a higher power than one of half-inch focus, or thereabouts, and before trying this, they should familiarise themselves with the use of one with an inch focus.
It is a popular error to suppose that enormous magnification is always an advantage, and that a microscope is valuable because it makes a flea look as big as a cat or a camel. The writer has often smiled at the exclamations of casual visitors, who have been pleased with his microscopic efforts to entertain them. "Dear me, what a wonderful instrument; it must be immensely powerful;" and so forth. These ejaculations have often followed the use of a low power, and their authors have been astonished at receiving the explanation that the best microscope is that which will show the most with the least magnification, and that accuracy of definition, not mere increase of bulk, is the great thing needful.
Scientific men always compute the apparent enlargement of the object by one dimension only. Thus, supposing an object one hundredth of an inch square were magnified so as to appear one inch square, it would, in scientific parlance, be magnified to "one hundred diameters," or one hundred linear; and the figures 100 would be appended to any drawing which might be made from it. It is, however, obvious that the length is magnified as well as the breadth; and hence the magnification of the whole surface, in the instance specified, would be one hundred times one hundred, or ten thousand: and this is the way in which magnification is popularly stated. A few moments' consideration will show that the scientific method is that which most readily affords information. Any one can instantly comprehend the fact of an object being made to look ten times its real length; but if told that it is magnified a hundred times, he does not know what this really means, until he has gone through the process of finding the square root of a hundred, and learnt that a hundredfold magnification means a tenfold magnification of each superficial dimension. If told, for example, that a hair is magnified six hundred diameters, the knowledge is at once conveyed that it looks six hundred times as broad as it is; but a statement that the same hair is magnified three hundred and sixty thousand times, only excites a gasping sensation of wonder, until it is ascertained by calculation that the big figures only mean what the little figures express. In these pages the scientific plan will always be followed.
If expense is not an object, a binocular instrument should be purchased, and it is well to be provided with an object-glass as low as three or even four inches focus, which will allow the whole of objects having the diameter of half an inch or more to be seen at once. Such a low power is exceedingly well adapted for the examination of living insects, or of the exquisite preparations of entire insects, which can now be had of all opticians. Microscopes which have a draw tube can be furnished with an erector, an instrument so called because it erects the images, which the microscope has turned upside down, through the crossing of the rays. This is very convenient for making dissections under the instrument; and it also gives us the means of reducing the magnifying power of an object-glass, and thus obtaining a larger field. The erector is affixed to the end of the draw tube, and by pulling it out, or thrusting it in, the rays from the object-glass are intercepted at different distances, and various degrees of power obtained.
A binocular microscope is most useful with low powers from two thirds upwards. A new form, devised by Mr. Stephenson, acts as an erector, and is very valuable for dissections. It works with high powers.
Beginners will be glad to know how to obtain the magnifying power which different objects require, and it may be stated that, with a full-sized microscope, a two-inch object-glass magnifies about twenty-five diameters with the lowest eye-piece; a one-inch object-glass, or two thirds, from fifty to sixty diameters; a half-inch about one hundred; a quarter-inch about two hundred. The use of deeper eye-pieces adds very considerably to the power, but in proportions which differ with different makers. One instrument used by the writer has three eye-pieces, giving with a two thirds object-glass powers of sixty one hundred and five, and one hundred and eighty respectively; and with a fifth two hundred and forty, four hundred and thirty, and seven hundred and twenty, which can be augmented by the use of a draw tube.
It has been well observed that the illumination of objects is quite as important as the glasses that are employed, and the most experienced microscopists have never done learning in this matter. Most microscopes are furnished with two mirrors beneath the stage, one plane and one concave. The first will throw a few parallel rays through any transparent object properly placed, and the latter causes a number of rays to converge, producing a more powerful effect. The first is usually used in daylight, when the instrument is near a window (one with a north aspect, out of direct sunlight, being the best); and the second is often useful when the source of illumination is a candle or a lamp. By varying the angle of the mirror the light is thrown through the object more or less obliquely, and its quantity should never be sufficient to pain the eye. Few objects are seen to the best advantage with a large pencil of perfectly direct light, and the beginner should practise till the amount of inclination is obtained which produces the best effect.
It is advisable that the hole in the stage of the microscope should be large—at least an inch and a half each way—so that the entrance of oblique rays is not obstructed, and it is desirable that the mirror, in addition to sliding up and down, should have an arm by which it can be thrown completely out of the perpendicular plane of the body of the instrument. This enables such oblique rays to be employed as to give a dark field, all the light which reaches the eye being refracted by the object through which it is sent. The opticians sell special pieces of apparatus for this purpose, but though they are very useful, they do not render it less desirable to have the mirror mounted as described.
Most microscopes are furnished with a revolving diaphragm, with three holes, of different sizes, to diminish the quantity of light that is admitted to the object. This instrument is of some use, and offers a ready means of obtaining a very soft agreeable light for transparent objects, viewed with low powers. For this purpose cut a circular disk of India or tissue paper, rather larger than the biggest aperture; scrape a few little pieces of spermaceti, and place them upon it, then put the whole on a piece of writing-paper, and hold it a few inches above the flame of a candle, moving it gently. If this is dexterously done, the spermaceti will be melted without singeing the paper, and when it is cold the disk will be found transparent. Place it over the hole in the diaphragm, send the light through it, and the result will be a very soft agreeable effect, well suited for many purposes, such as viewing sections of wood, insects mounted whole, after being rendered transparent, many small water creatures, etc. Another mode of accomplishing this purpose is to place a similarly prepared disk of paper on the flat side of a bull's-eye lens, and transmit the light of a lamp through it. This plan may be used with higher powers, and the white opaque light it gives may be directed at any angle by means of the mirror beneath the stage.
An ordinary lamp may be made to answer for microscopic use, but one of the small paraffine lamps now sold everywhere for eighteen-pence is singularly convenient. It is high enough for many purposes, and can easily be raised by one or more blocks. A paraffine lamp on a sliding stand is still more handy, and all the better for a hole with a glass stopper, through which the fluid can be poured.
Many people fancy that the eyes are injured by continual use of the microscope, but this is far from being the case if reasonable precautions are taken. The instrument should be inclined at a proper angle, all excess of light avoided, and the object brought into focus before it is steadily looked at. Most people solemnly shut one eye before commencing a microscopic examination; this is a practical and physiological mistake. Nature meant both eyes to be open, and usually resents a prolonged violation of her intentions in this matter. It requires but a little practice to keep both eyes open, and only pay attention to what is seen by that devoted to the microscope. The acquisition of this habit is facilitated, and other advantages gained, by a screen to keep out extraneous light. For this purpose take a piece of thin cardboard about nine inches square, and cut a round hole in it, just big enough to admit the tube of the microscope, about two inches from the bottom, and equidistant from the two sides. Next cut off the two upper corners of the cardboard, and give them a pleasant-looking curve. Then cover the cardboard with black velvet, the commonest, which is not glossy, answers best, and your screen is made. Put the hole over the tube of the microscope, and let the screen rest on the little ledge or rim which forms an ornamental finish to most instruments. A piece of cork may be gummed at the back of the screen, so as to tilt it a little, and diminish its chance of coming into contact with that important organ the nose. This little contrivance adds to the clearness and brilliancy of objects, and is a great accommodation to the eyes.
One more oculistic memorandum, and we have done with this chapter. Do not stare at portions of objects that are out of focus, and consequently indistinct, as this injures the eyes more than anything. Remember the proverb, "None so deaf as those that won't hear," which naturally suggests for a companion, "None so blind as those that won't see." It is often impossible to get every object in the field in focus at one time;—look only at that which is in focus, and be blind to all the rest. This is a habit easily acquired, and is one for which our natural microscopes are exceedingly grateful; and every judicious observer desires to keep on the best terms with his eyes.
CHAPTER II.
JANUARY.
Visit to the ponds—Confervæ—Spirogyra quinina—Vorticella—Common Rotifer—Three divisions of Infusoria—Phytozoa—Protozoa—Rotifera—Tardigrada—Meaning of these terms—Euglenæ—Distinction between animals and vegetables—Description of Vorticellæ—Dark ground illumination—Modes of producing it—The Nucleus of the Vorticellæ—Methods of reproduction—Ciliated Protozoa—Wheel bearers or Rotifers—Their structure—The common Rotifer—The young Rotifer seen inside the old one—An internal nursery—"Differentiation" and "Specialisation"—Bisexuality of Rotifers—Their zoological position—Diversities in their appearance—Structure of their Gizzard—Description of Rotifers.
HE winter months are on the whole less favorable to the collection of microscopic objects from ponds and streams than the warmer portions of the year; but the difference is rather in abundance than in variety, and with a very moderate amount of trouble, representatives of the principal classes can always be obtained.
On a clear January morning, when the air was keen, but no ice had yet skinned over the surface of the water, a visit to some small ponds in an open field not far from Kentish Town provided entertainment for several days. The ponds were selected from their open airy situation, the general clearness of their water, and the abundance of vegetation with which they were adorned. Near the margin confervæ abounded, their tangled masses of hair-like filaments often matted together, almost with the closeness of a felted texture. At intervals, minute bubbles of air, with occasionally a few of greater size, indicated that the complex processes of vegetable life were actively going on, that the tiny plants were decomposing carbonic acid, dexterously combining the carbon—which we are most familiar with in the black opaque form of charcoal—to form the substance of their delicate translucent tissues, and sending forth the oxygen as their contribution to the purification of the adjacent water, and the renovation of our atmospheric air. This was a good sign, for healthy vegetation is favorable to many of the most interesting forms of infusorial life. Accordingly the end of a walking-stick was inserted among the green threads, and a skein of them drawn up, dank, dripping, and clinging together in a pasty-looking mass. To hold up a morsel of this mass, and tell some one not in the secrets of pond-lore that its dripping threads were objects of beauty, surpassing human productions, in brilliant colour and elegant form, would provoke laughter, and suggest the notion that you were poking fun at them, when you poked out your stick with the slimy treasure at its end. But let us put the green stuff into a bottle, with some water from its native haunt, cork it up tight, and carry it away for quiet examination under the microscope at home.
Here we are with the apparatus ready. We have transferred a few threads of the conferva from the bottle to the live box, spreading out the fine fibres with a needle, and adding a drop of water. The cover is then gently pressed down, and the whole placed on the stage of the microscope, to be examined with a power of about sixty. A light is thrown somewhat obliquely by the mirror through the object, the focus adjusted, and a beautiful sight rewards the pains. Our mass of conferva turns out to contain one of the most elegant species. Fine hair-like tubes of an organic material, as transparent as glass, are divided by partitions of the same substance into cylindrical cells, through which a slender ribbon of emerald green, spangled at intervals with small round expansions, is spirally wound. We shall call it the Spiral Conferva, its scientific name being Spirogyra quinina. Some other species, though less elegantly adorned, make a pleasing variety in the microscopic scene; and appended to some of the threads is a group of small crystal bells, which jerk up and down upon spirally twisted stalks. These are the "Bell Flower Animalcules" of old observers, the Vorticellæ, or Little Vortex-makers of the present day. Other small creatures flit about with lively motions, and among them we observe a number of green spindles that continually change their shape, while an odd-looking thing crawls about, after the manner of certain caterpillars, by bringing his head and tail together, shoving himself on a step, and then repeating the process, and making another move. He has a kind of snout, behind which are two little red eyes, and something like a pig-tail sticks out behind. This is the Common Wheel-bearer, Rotifer vulgaris, a favourite object with microscopists, old and young, and capable, as we shall see, of doing something more interesting than taking the crawl we have described.
A higher power, say one or two hundred, may be conveniently applied to bring out the details of the inhabitants of our live box more completely; but if the glasses are good, a linear magnification of sixty will show a great deal, with the advantage of a large field, and less trouble in following the moving objects of our search.
Having commenced our microscopic proceedings by obtaining some Euglenæ, Vorticellæ, and a Rotifer, we are in a position to consider the chief characteristics of three great divisions of infusoria, which will often engage our attention.
It is well known that animalcules and other small forms of being may be found in infusions of hay or other vegetable matter, and hence all such and similar objects were called Infusoria by early observers. Many groups have been separated from the general mass comprehended under this term, and it is now used in various senses. The authors of the 'Micrographic Dictionary' employ it to designate "a class of microscopic animals not furnished with either vessels or nerves, but exhibiting internal spherical cavities, motion effected by means of cilia, or variable processes formed of the substance of the body, true legs being absent." The objection to this definition is, that it to some extent represents theories which may not be true. That nerves are absent all through the class is an assumption founded merely upon the negative evidence of their not having been discovered, and the complete absence of "vessels" cannot be affirmed.
In the last edition of 'Pritchard's Infusoria,' to which some of our ablest naturalists have contributed, after separating two groups, the Desmids, and the Diatoms, as belonging to the vegetable world, the remainder of the original family of infusoria are classified as Phytozoa, Protozoa, Rotifera, and Tardigrada. We shall explain these hard names immediately, first remarking that the Desmids and the Diatoms, concerning whom we do not intend to speak in these pages, are the names of two groups, one distinctly vegetable, while the other, although now generally considered so, were formerly held by many authorities to be in reality animal. The Desmids occur very commonly in fresh water. We have some among our Confervæ. They are most brilliant green, and often take forms of a more angular and crystalline character than are exhibited by higher plants. The Diatoms are still more common, and we see before us in our water-drop some of their simplest representatives in the form of minute boats made of silica (flint) and moved by means still in dispute.
Leaving out the Desmids and Diatoms, we have said that in Pritchard's arrangement the views of those writers are adopted who divide the rest of the infusoria into four groups, distinguished with foreign long-tailed names, which we will translate and expound. First come the Phytozoa, under which we recognise our old acquaintance zoophyte turned upside down. Zoophytes mean animal-plants, Phytozoa mean plant-animals. We shall have by-and-bye to speak of some of the members of this artificial and unsatisfactory group, and postpone to that time a learned disquisition on the difference between animals and plants, a difference observable enough if we compare a hippopotamus with a cabbage, but which "grows small by degrees, and beautifully less," as we contemplate lower forms.
After the Phytozoa come the Protozoa, or first forms in which animality is distinctly recognised. Under this term are assembled creatures of very various organization, from the extreme simplicity of the Proteus or Amœba, a little lump of jelly, that moves by thrusting out portions of its body, so as to make a sort of extempore legs, and in which no organs can be discerned,[2] up to others that are highly developed, like our Vorticellæ. This group is evidently provisional, and jumbles together objects that may be widely separated when their true structure and real affinities are discerned.
[2] In some kinds and in some stages of growth this is not strictly true.
Following the Protozoa, come the Rotifera, or Wheel-bearers, of which we have obtained an example from our pond, and whose characteristics we shall endeavour to delineate when our specimen is under view; and last in the list we have the Tardigrada, "Slow-steppers," or Water Bears, queer little creatures, something like new-born puppies, with a double allowance of imperfect feet. These, though somewhat connected with the rotifers, are considered to belong to a low division of the arachnida (spiders, &c.).
a, motile; and b, resting condition of Euglenæ.
Feeling that we must be merciful with the long-tailed words and explanations of classification, we reserve further matter of this kind for the opportunities that must arise, and direct our attention to living forms by watching the Euglenæ which our water-drop contains. We have before us a number of elegant spindle-shaped bodies, somewhat thicker in front than behind, and in what may be called the head there glitters a brilliant red speck, commonly called an eye-spot, although, like the eyes of potatoes, it cannot see. Round this eye-spot the tissues are clear, like glass; but the body of the creature is of a rich vegetable green, which shines and glistens as it catches the light. Some swim rapidly with a rollicking motion, while others twist themselves into all manner of shapes. Now the once delicate spindle is oddly contorted, now it swells out in the middle, like a top, and now it rolls itself into a ball. The drawings will afford some idea of these protean changes, but they must be seen before their harlequin character can be thoroughly appreciated. Some of the specimens exhibit delicate lines running lengthwise, and taking a spiral twist as the creature moves about; but in none can any mouth be discerned, and their antics, although energetic and comical, afford no certain indications of either purpose or will. What are they? animals or vegetables? or something betwixt and between?
The first impression of any casual observer would be to declare in favour of their animality; but before this can be settled, comes the question, what is an animal, and how does it differ from a vegetable? and upon this the learned do by no means agree. One writer considers the presence of starch in any object a proof that it belongs to the dominions of Flora, while another would decide the issue by ascertaining whether it evolves oxygen and absorbs carbon, as most plants do, or whether it evolves carbon and absorbs oxygen, as decided animals do. Dr. Carpenter asserts that the distinction between Protophyta and Protozoa (first or simplest plants and animals), "lies in the nature of their food, and the method of its introduction, for whilst the Protophyte obtains the materials of its nutrition from the air and moisture that surround it, and possesses the power of detaching oxygen, hydrogen, carbon, and nitrogen from their previous binary combinations, and of uniting them into ternary and quaternary organic compounds (chlorophyll, starch, albumen, &c.), the simplest Protozoa, in common with the highest members of the animal kingdom, seems utterly destitute of any such power, makes, so to speak, a stomach for itself in the substance of its body, into which it injects the solid particles that constitute its food, and within which it subjects them to a regular process of digestion."
Unfortunately it is very difficult to apply this simple theory to the dubious objects which lie on the border-land of the animal world, and no other theory that has been propounded appears to meet all cases. Some naturalists do not expect to find a broad line of demarkation between the two great divisions of living things, but others characterise such an idea as "unphilosophical," in spite of which, however, we incline towards it.
Mr. Gosse, whose opinion is entitled to great respect, calls the Euglenæ "animals" in his 'Evenings with the Microscope;' but from the aggregate of recorded observations it seems that they evolve oxygen, are coloured with the colouring matter of plants, reproduce their species in a manner analogous to plants, and have in some cases been clearly traced to the vegetable world. It is, however, possible that some Euglenæ forms may be animal and others vegetable, and while their place at nature's table is being decided, they must be content to be called Phytozoa, which, as we have before explained, is merely Zoophyte turned upside down.
Some authorities have thought their animality proved by the high degree of contractility which their tissues evince. This, however, cannot go for much, as all physiologists admit contractility to belong to the vegetable tissues of the sensitive plant, "Venus' Fly-trap," &c., and a little more or less cannot mark the boundary between two orders of being.
We shall have occasion again to notice the Protophytes, and now pass to the Protozoa, of which we have a good illustration in the Vorticella already spoken of. In the group before us a number of elegant bells or vases stand at the end of long stalks, as shown at the top of the frontispiece, while round the tops of the bells, the vibrations of a wreath or cilia produce little vortices or whirlpools, and hence comes the family name. This current brings particles of all sorts to the mouth near the rim of the bells, and the creature seems not entirely destitute of power to choose or reject the morsels according to its taste. Every now and then the stalk of some specimen is suddenly twisted into a spiral, and contracted, so as to bring the bell almost to the ground. Then the stem gracefully elongates again, and the cilia repeat their lively game.
The general effect can be seen very well by a power of about sixty linear, but one of them from one to two hundred is necessary to bring out the details, and a practised observer will use still more magnification with good effect. They should be examined by a moderately oblique light, or most of the cilia are apt to be rendered invisible, and also by dark ground illumination. This may be accomplished in a well-made microscope by turning the mirror quite out of the plane of the axis of the instrument, that is to say, on one side of the space the body would occupy if it were prolonged. By this means, and by placing the lamp at an angle with the mirror, that must be learnt by experiment, all the light that reaches the eye has first passed through the object, and is refracted by it out of the line it was taking, which would have carried it entirely away. Or the object may be illuminated by an apparatus called a spotted lens, which is a small bull's-eye placed under the stage, and having all the centre of its face covered with a plaster of black silk. In this method the central or direct rays from the mirror are obstructed, but those which strike the edge of the bull's-eye are bent towards the object, which they penetrate and illuminate if it is sufficiently transparent and refractive. Another mode of dark ground illumination is by employing an elegant instrument called a parabolic illuminator, which need not be described.
Left: Vorticella, with posterior circlet of cilia in process of separation—Stein.
Right: Vorticella in process of self-division. A new frontal wreath in formation in each of the semi-lunar spaces.
Different specimens and species of Vorticellæ vary in the length of their bells from one three or four thousandth to one hundred and twentieth of an inch, and when they are tolerably large, the dark ground illumination produces a beautiful effect. The bells shine with a pearly iridescent lustre, and their cilia flash with brilliant prismatic colours.
Left: Vorticella microstoma, showing alimentary tube, ciliated mouth, and formation of a gemma at the base, 300 linear.—Stein.
Right: Vorticella microstoma, the encysted animal protruding through a supposed rupture of the tunic.
The Vorticellina belong to the upper division of the Protozoa—the ciliata, or ciliated animalcules, and they have a mouth, an œsophagus, and an orifice for the exit of their food.
Many observers used to ascribe to those creatures a complete intestinal canal, but such an apparatus is now believed not to exist in any of the Infusoria. Food particles, after leaving the œsophagus, are thrust forward into the sarcode, or soft flesh, and any cavity thus formed acts as a stomach.
The bells or cups are not, as might be fancied from a casual inspection, open like wineglasses at the top, but furnished with a retractile disk or cover, on which the cilia are arranged. Their stalks are not simple stems, but are hollow tubes, which in the genus Vorticella are furnished with a muscular band, by whose agency the movements are principally made.
Some of the Vorticellids will be observed to leave their stalks, having developed cilia round their base, and may be seen to swim about in the enjoyment of individual life. They are also capable of becoming encysted, that is, of secreting a gelatinous cover.
Encysted Vorticella, showing the obliteration of special organs by the advancement of the process.—Pritchard.
These changes are exhibited in the annexed cuts, which are copied from known authorities. By careful observation of the bodies of Vorticellids, a contractile vesicle may be observed, which appears to cause a movement of fluids, that is probably connected either with respiration or secretion.
Another piece of apparatus in this family, but not confined to it, is the so-called nucleus, which in this case is of a horseshoe shape and granular texture, and greater solidity than the surrounding parts. The functions of this organ formed the subject of various conjectures, but it is now generally held to be an ovary.
Vorticella microstoma, in process of encystment, 300 linear; in the last the inclosing tunic is plainly developed.—Stein.
In common with many of the lower animals, the Vorticellids have three ways of multiplying their race. One by fission, or division of their bodies: another by buds, somewhat analogous to those of plants; and another by reproductive germs. These processes will come again under our notice, and we shall leave the Vorticellids for the present by observing that if they are fed with a very small quantity of indigo or carmine, the vacuoles or spaces, into which their nutriment passes, will be clearly observed. Ehrenberg thought in these and similar creatures that every vacuole was a distinct stomach, and that all the stomachs were connected by an intestinal canal; hence his name Polygastrica, or many stomached. In these views he has not been followed by later observers, and it is probable he was misled, partly by pushing the process of reasoning from the analogies of higher animals much too far, and partly by the imperfection of the glasses he employed.
Rotifer vulgaris.—A, mouth, or gizzard; B, contractile vesicle.—Micrographic Dictionary.
N.B.—When the cilia and tail part are retracted, and the body shortened, the creature assumes an obtuse oval form.
Having thus briefly considered the Vorticellids we must turn to the wheel-bearer, who belongs to a higher race than even the ciliated Protozoa. We left her crawling about with her snout or proboscis protruded, but now she has moored herself by her tail-foot, pulled in her nose, and put out two groups of cilia, which look like revolving wheels, and a little below them is seen a gizzard in a state of active work. After a little while she swims away with her wheels going, and her tail, forked at the end, is found to be telescopic, or capable of being pulled in and out. As the cilia play, the neighbouring water is agitated, and the multitudes of small objects are brought by the whirlpools within her ravenous maw. But the strangest thing of all is that inside her body is seen a young one; in this case a large and fine infant, which, like "a chip of the old block," imitates the parental motions, thrusts forth its cilia and works its gizzard.[3] In other genera the eggs are hatched externally, but this one is ovoviparous, and carries its nursery inside.
[3] This was met with in the summer, but is described here to avoid repetition. I do not know whether the eggs are hatched in very cold weather.
A very slight investigation is sufficient to show that in the wheel-bearer we have made a great advance towards a higher organization than we discovered in the preceding creatures. We witness what the learned call a "differentiation" of parts and tissues, and a "specialization" of organs. The head is plainly distinguishable from the body, the skin or integument is distinctly different from the internal tissues, behind the eyes we can detect a nervous ganglion or miniature brain, the gizzard is a complicated piece of vital mechanism, such as we have not met with before, and in various parts of the transparent inside we see organs to which particular functions are assigned.
It was at one time thought that Rotifers were hermaphrodite—uniting both sexes in one body—but that idea is now generally abandoned, for in many species the males have been discovered, and the fair sex may be gratified to hear that they are without doubt the "inferior animals." Their function is simply to assist the female in producing young, and as this can be quickly accomplished, their lives are short, and they are not supplied with the gizzard and digestive apparatus, which their lady-loves possess. Much discussion has taken place as to the rank which the Rotifers hold in the animal kingdom, some naturalists thinking them relations of the crabs, and others believing them to belong to the family of the worms. Professor Huxley, who adopts the latter view, which has the most friends, groups the lower Annulosa together under the name of Annuloida, in which he includes Annelides, or worms of various kinds, the Echinodermata (or "spine skins," among which are the star-fish and sea hedgehogs), and some other families. He considers the Rotifers to be "the permanent forms of Echinoderm larvæ." This does not mean that they were ever produced by Echinoderms, and had their development checked, but that they resemble them in organization, and illustrate a general law, observable in animated beings, namely, that the lower creatures are like the imperfect stages of higher animals, and that all things are formed according to general principles, and exhibit a uniformity of plan.
Mr. Gosse adopts a different view, and while admitting a connection between the Rotifers and the worms, adduces important reasons for associating them with the insects.
Leaving zoologists to settle their position, we may remark that the Rotifers form a very numerous family, presenting very great diversities of structure, some of the most interesting of which we shall meet with in the course of our rambles; but they all possess a gizzard, which, though differing in complexity, is throughout formed upon the same principle, and that we must now explain.
We have called the masticatory apparatus of the Rotifers a gizzard; but Mr. Gosse, who has done most to elucidate its structure, contends that it is a mouth; and in some species it is frequently protruded, and used like the mouth of higher animals. Taking one of the most typical forms of this organ, and drawing our illustrations from Mr. Gosse's admirable paper in the "Transactions of the Royal Society," we may describe it, when completely developed, as consisting of three lobes, having a more or less rounded form. The eminent naturalist we have named calls the whole organ the mastax, and states that it is composed of dense muscular fibre. The tube which leads down to it he designates the "buccal (mouth) funnel," and the tube that issues from it, and conveys the food to the digestive sac or stomach, he calls the œsophagus, in conformity with the nomenclature applied to creatures whose mouths are in the usual place. Inside the mouth-gizzard are placed two organs, which work like hammers, and which Mr. Gosse therefore names mallei. The hammers work against a sort of anvil, which is called incus, the Latin for that implement. Each hammer consists of two portions articulated by a hinge joint. The lower portion, the manubrium, or handle, gives motion to the upper portion, which from its shape is named the uncus, or hook. The unci are furnished with finger-like processes of teeth, which vary in number. There are five or six in the best developed specimens. These hooks or teeth work against each other, and against the incus, or anvil, which consists of distinct articulated portions, of which the principal are two rami, or branches, jointed so that they can open and close like a pair of shears. These two rest upon the third portion, which is called the fulcrum. Some faint idea of the working of the toothed hammers may be obtained by rubbing the knuckles of both hands together, but the motion is more complicated, and the rami play their part in the trituration of the food. Mr. Gosse states that when an objectionable morsel has got as far as this mouth-gizzard, "it is thrown back by a peculiar scoop-like action of the unci, very curious to witness." The foregoing diagram will help the reader to comprehend this description, but no opportunity should be lost for viewing this remarkable organ busy at work in the living animals.
Gizzard of Notomata.
The respiration of the Rotifers is supposed to be effected by the passage of water through vessels running round them, and called the "water vascular system," and in addition to their eyes, which often disappear in adult specimens, the organ we described as standing out like a pig-tail, as our acquaintance crawled along, is thought to act as an antenna, or feeler, and brings its possessor in further relation to the external world. It is also called the calcar, or spur, and is furnished with cilia or bristles at its extremity.
Sometimes the particles swallowed by the Common Rotifer are large enough for their course to be traced, but there is frequently a great commotion and grinding of the gizzard, without any appreciable cause, although doubtless something is taken in, and when the creature is tired, or has had enough, we see both head and tail retracted, and the body assumes a globular form. In another chapter, when viewing a Philodine, we shall see how in the family to which the Common Rotifer belongs, the gizzard departs from the perfect type.
CHAPTER III.
FEBRUARY.
Visit to Hampstead—Small ponds—Water-fleas—Water-beetle—Snails—Polyps—Hydra viridis—The dipping-tube—A glass cell—The Hydra and its prey—Chydorus sphæricus and Canthocamptus, or friends and their escapes—Cothurnia—Polyp buds—Catching Polyps—Mode of viewing them—Structure of Polyps—Sarcode—Polyps stimulated by light—Are they conscious?—Tentacles and poison threads—Paramecium—Trachelius—Motions of Animalcules, whether automatic or directed by a will—Their restless character.
T has been a bitterly cold night, and as the sun shines on a clear keen morning, and glistens in the hoar-frost which covers the trees, it might seem an unpropitious time for visiting the ponds, in search of microscopic prey. We will, however, try our luck, and take a brisk trot to the top of Hampstead Heath, where the air is still keener, and the ice more thick. Arriving at the highest point, London appears on one side enveloped in its usual great coat of smoke, through which St. Paul's big dome, with a score or two of towers and steeples, can be dimly made out; while looking towards Harrow-on-the-Hill, or Barnet, we see the advantage of country air in the sharpness with which distant objects cut the blue sky. We leave the large ponds for another time, and hunt out the little hollows among the furze and fern. One looks promising from the bright green vegetation to be discovered under the sheet of ice, which is almost firm enough to bear human weight.
Breaking a convenient hole we hook up some of the water-plants, and place them in a wide-mouthed vial, which we fill with water, and cursorily examine with a pocket-lens. Some water-fleas briskly skipping about, and a beautiful little beetle, with an elegant dotted pattern on his brown back, and a glistening film of air covering his belly, show that we have not been unsuccessful, although we must wait till we get home to know the extent of our findings, among which, however, we can only discern the graceful spiral shell of a small water-snail, the Planorbis.
Arriving at home the bottle was left undisturbed for some hours in a warm light place, and then on being examined several specimens of that beautiful polyp, the Hydra viridis, were seen attached to the glass, and spreading their delicate tentacles in search of prey. One of the polyps is carefully removed by the dipping-tube, a small glass tube, open at both ends. The forefinger is placed upon the top, and when the other end is brought over the object the finger is raised for an instant, and as the water rushes in the little hydra comes too, and is placed in a glass cell, about half an inch wide, and one tenth of an inch deep. These cells are obtained from the opticians, and cemented with varnish or marine glue to an ordinary glass slide. After an object has been placed in one of them, a little water is taken up in the dipping-tube, and the cell filled until the fluid stands in a convex heap above its brim. We then select around glass cover, and press it gently on the walls of our cell. A few drops of superfluous water escape, and we have the cell quite full, and the cover held tight by force of the capillary attraction between the water and the glass.
Hydra viridis with developed young one, and bud beginning to sprout.
The polyp deposited in one of these water cages is then transferred to the stage of the microscope, and its proceedings watched. At first it looks like a shapeless mass of apple-green jelly. Soon, however, the tail end of the creature is fixed to the glass, the body elongates, and the tentacles (in this case eight) expand something after the manner of the leaves of a graceful palm.
By accident two small Water Fleas were imprisoned with the polyp, and one (a shrimp-like looking creature, carrying behind her a great bag of eggs) came into contact with the tentacles, and seemed paralysed for a time. The hydra made no attempt to convey the captive to its mouth, but held it tight until another Water Flea, a round merry little fellow (Chydorus sphæricus), came to the rescue, and assisted Canthocamptus to escape by tugging at her tail. This friendly action may not have been prompted by the intelligence which seemed to suggest it, but those who have kept tame soldier-crabs and prawns in an aquarium, will not be indisposed to attribute to the crustaceans more brains than they have usually credit for. It must, however, be confessed that the subsequent conduct of Mrs. Canthocamptus did not indicate the possession of much prudence, for she learnt no lesson from experience, but repeatedly swam against her enemy's tentacles, suffered many captures, and only escaped being devoured through the indifference, or want of appetite, which the polyp evinced.
A, Canthocamptus minutus; B, Chydorus sphæricus; C and D, Capsules and poison-thread of polyp; E, Tricodina pediculus, side view and under view; F, Kerona polyporum.—Microg. Dict.
On the body of the Canthocamptus were some small transparent vases or bottles, containing living objects, which sprang up and down. These were members of the Vorticella family, called Cothurnia, and will be hereafter described.
Hydra viridis, in various shapes.
Watching the hydra it was curious to note the changes of form which these creatures are able to assume. Now the tentacles were short and thick, and the body squat; now the body was elongated, like the stem of a palm tree, and the tentacles hung gracefully from the top. From some of the polyps little round buds were growing, while other buds were already developed into miniature copies of the parent, and only attached by a slender stalk. In a few days many of these left the maternal side, fixed their own little tails to the glass, and commenced housekeeping on their own account.
Polyps may be obtained at all times of the year by bringing home duckweed, conferva, and other water-plants from the ponds. Some hauls may be unsuccessful, but if one pond is not propitious others should be tried. The plants should be put in a capacious vessel of water, and placed in the light, where, if polyps be present, they will show themselves within twenty-four hours, either attached to the sides of the glass, or hanging from the plants, or suspended head downwards from the upper film of the water. They are elegant objects, and may be kept without difficulty for some weeks. After being confined in a small quantity of water for purposes of examination, they should be carefully replaced in the larger vessel, and may thus be used again and again without suffering any injury. A low power—a three or two-inch glass—or a one-inch, reduced by employing the erector—is the most convenient for examining the whole creature, but higher powers are necessary to make out its minute structure. They should be viewed with direct and oblique light, as transparent and also as opaque objects. In the latter case the "Lieberkuhn," or polished silver speculum, is convenient, and if the microscope is not furnished with Lister's dark wells, a small piece of black paper may be stuck behind the object, by simply wetting it with the tongue.[4]
[4] The side silver reflector is useful for illuminating such objects.
Although the polyps are remarkable for the simplicity of their organization, they do not the less exhibit the wonderful nature of animal life. Their bodies are composed of the substance, called sarcode, in which is imbedded a colouring matter resembling that in the leaves of plants; every part possesses irritability and contractility, and they are very sensitive to the stimulus of light. The outer layer of their bodies is harder than the inner layer. These layers are severally called ectoderm and endoderm. They may be cut and grafted like trees, and if turned inside out, the new inside digests and assimilates as well as the old. Whether any form of consciousness can belong to creatures which have no distinct nervous system is open to doubt, but it would seem probable from their movements that food and light afford them something like a pleasurable sensation in a very humble degree. If we were sufficiently acquainted with the secrets of molecular combination we might discover that the various functions of these simple organisms were discharged by different particles, although it is only in higher creatures that muscular particles are aggregated into muscles, or nerve particles into nerves.
Having examined the general appearance and proceedings of the hydra, let us cut off a tentacle, or take a small specimen and gently crush it by pressing down the cover of the live box, and place the object so prepared under a power of about three hundred linear. If we then illuminate it with a moderate quantity of oblique light, we shall discover round the edge of the tentacle a number of small cells or capsules, from some of which a very slender wire or thread will be emitted.[5] These are the stinging organs of the polyp, and resemble those which Mr. Gosse has so ably elucidated in the sea anemones. Some writers have endeavoured to show that they are not stinging organs at all, but so large an amount of evidence to the contrary is accumulated in Mr. Gosse's 'Actinologia Britannica,' that no reasonable doubt remains. The stinging capsules of the polyp are shown in the annexed sketch, and also the way in which they are employed, for it fortunately happened that on exposing one of the hydras to pressure in the live box, a small worm (Anguillula) escaped, which had been pierced with the minute weapons which are supposed to convey a poison into the wound. The authors of the 'Micrographic Dictionary' think that the prongs of the forks, which will be seen to point upwards in the sketch,[6] are springs, and occupy a reversed position in the capsule cells, and that their function is to throw out the threads. However this may be, the polyps, and similarly endowed creatures, have the power of darting out their poison threads with considerable force, and Mr. Gosse found that the anemone was able to pierce a thick piece of human skin.
Anguillula pierced by stinging organs of the Hydra viridis.
The same excellent observer attributes the emission of the anemone poison threads, which he considers hollow, to the injection of a fluid. In their quiescent state, he thinks they are drawn in, like the finger of a glove, and are forced out as the liquid enters their slender tubes. Possibly the polyp stinging organs may have the same structure.
Notwithstanding their dangerous weapons, polyps are often infested with a parasite, the Trichodina pediculus, as shown in Fig. E, page 49, and it must happen that either this visitation is not disagreeable, or that the Trichodina is not influenced by the poison.
As the plants in the bottles decayed, some of the animalcules died off and others appeared. In one bottle, containing decaying chara, Paramecia abounded. The Paramecia, of which there are various species, have always been favourite objects with microscopists. The Germans call them "slipper animalcules," and they vary in size from 1—96" [7] to 1—1150". They are flat rounded-oblong creatures, with a distinct integument or skin, "through which numerous vibratile cilia pass in regular rows."[8] They are furnished with a distinct mouth, and adult specimens exhibit star-shaped contractile vesicles in great perfection.
[7] The usual mode of giving dimensions is by fractions thus expressed: 1—96" means one ninety-sixth of an inch.
[8] 'Micrographic Dictionary.'
The swarm of specimens before us belong to one species, Paramecium aurelia, the Chrysalis animalcule, and they crowd every portion of the little water-drop we have taken up, and examined with a power of about one hundred linear. When they are sufficiently quiet a power of about four hundred may be used with advantage, and Pritchard recommends adding a little indigo and carmine to the water, in order to see the cilia more clearly, or rather to render their action more plain. The cilia are disposed lengthwise, and Ehrenberg counted in some rows sixty or seventy of them, making an aggregate of three thousand six hundred and forty organs of motion in one small animated speck. This number seems large, but although we have never performed the feat of counting them, we should have expected it to prove much greater. Unlike most animalcules they are susceptible of being preserved by drying upon glass, and we subjoin a figure from Pritchard, of one thus treated, in which the star-shaped vesicles are clearly seen. These curious organs communicate with other vessels, and, as we have previously stated, are probably connected with respiration and excretion.
Paramecium aurelia. A dried specimen showing the vesicles.—Pritchard.
The genus Paramecium is now confined to those creatures which exhibit rows of longitudinal cilia of uniform length, which are destitute of hooks, styles, or other organs of motion than the cilia, which have a lateral mouth, and no eye-spots. One mode of increase is by division, which may be easily observed; another is through the formation of true eggs as traced by Balbiani.
Another of the treasures from the pond was a species of Trachelius, or long-necked ciliated animalcule, which kept darting in and out of a slimy den, attached to the leaf of a water-plant. The body was stout and fish-shaped, the tail blunt, and the neck furnished with long conspicuous cilia, which enabled the advancing and retreating movements to be made with great rapidity. The motions of this creature exhibit more appearance of purpose and design than is common with animalcules, but in proportion as these observations are prolonged, the student will be impressed with the difficulty of assuming that anything like a reasoning faculty and volition, is proved by movements that bear some resemblance to those of higher animals, whose cerebral capacities are beyond a doubt. It is, however, almost impossible to witness motions which are neither constant nor periodic, without fancying them to be dictated by some sort of intelligence. We must, nevertheless, be cautious, lest we allow ourselves to be deceived by reasoning so seductive, as the vital operations of the lowest organisms may be merely illustrations of blind obedience to stimuli, in which category we must reckon food, and until we arrive at forms of being which clearly possess a ganglionic system, we have no certainty that a real will exists, even of the simplest kind; and perhaps we must go still higher before we ought to believe in its presence.
Ehrenberg was much struck with the restless character of many infusoria—whether he looked at them by day or by night, they were never still. In fact their motions are like the involuntary actions which take place in the human frame; and if attached to their bodies we observe cilia that never sleep, the living membrane of some of our own organs, the nose, for example, is similarly ciliated, and keeps up a perpetual though unconscious work.
CHAPTER IV.
MARCH.
Paramecia—Effects of Sunlight—Pterodina patina—Curious tail—Use of a Compressorium—Internal structure of Pterodina—Metopidia—Trichodina pediculus—Cothurnia—Salpina—Its three-sided box—Protrusion of its gizzard mouth.
HE Paramecia, noticed in the last chapter, have increased and multiplied their kind without any fear lest the due adjustment between population and food should fail to be preserved. A small drop of the scum from the surface of the water in their bottle is an astounding sight. They move hither and thither in countless numbers, seldom jostling, although thick as herrings in a tub, and in many portions of the field the process of self-fissure, or multiplication by division, is going on without any symptoms of discomfort on the part of the parent creature. This is an interesting sight, but we will not linger over it, for the sun is shining, and there is enough warmth in the air to make it probable that the ponds will be more prolific than in the cold winter months. Sunshine is a great thing for the microscopic hunter; it brings swarms of creatures to the surface, and the Rotifers are especially fond of its genial beams. Even if we imitate it by a bright lamp, we shall attract crowds of live dancing specks to the illuminated side of a bottle, and may thus easily effect their capture by the dipping-tube.
Pterodina patina.
This year the March sunshine was not lost, for on the third of that month I obtained a bottleful of conferva from a pond about a mile from my house, and lying at the foot of the Highgate hills. Water-fleas were immediately discovered in abundance, together with some minute worms, and a ferocious-looking larva covered with scales; but what attracted most attention was a Rotifer, like a transparent animated soup-plate, from near the middle of which depended a tail, which swayed from side to side, as the creature swam along. The head exhibited two little red eyes; two tufts of cilia rowed the living disk through the water, and the gizzard worked with a rapid snapping motion, that left no doubt the ciliary whirlpools had brought home no slender stores of invisible food. Sometimes the end of the tail acted as a sucker, and fixed the animal tightly to the glass, when the wheels were protruded, and the body swayed to and fro. Then the sucker action ceased, and as the creature swam away, a tuft of cilia was thrust out from the extremity of the tail. A power of one hundred linear was sufficient to enable the general nature of this beautiful object to be observed, but to bring out the details, much greater amplification was required, and this would be useless if the little fidget could not be kept still.
450 Pterodina patina—gizzard.
The size of the creature, whose name we may as well mention was Pterodina patina, rendered this practicable, but required some care. The longest diameter of the body, which was not quite round, was about 1—120", so that it was visible to the naked eye, and as a good many were swimming together, one could be captured without much difficulty, and transferred with a very small drop of water to the live-box. Then the cover had to be put on so as to squeeze the animal just enough to keep it still without doing it any damage, or completely stopping its motions. This was a troublesome task, and often a little overpressure prevented its success.
Some observers always use in these cases an instrument called a compressorium, by which the amount of pressure is regulated by a lever or a fine screw; but whether the student possess one or not, he should learn to accomplish the same result by dexterously manipulating a well-made live-box. We will suppose the Pterodina successfully caged, and a power of about one hundred and fifty linear brought to bear upon her, for our specimen is of the "female persuasion." This will suffice to demonstrate the disposition and relation of the several parts, after which one of from four hundred to five hundred linear may be used with great advantage, though in this case the illumination must be carefully adjusted, and its intensity and obliquity frequently changed, until the best effect is obtained.
We find, on thus viewing the Pterodina, that it is a complex, highly organized creature, having its body protected by a carapace, like the shell of a tortoise, but as flexible as a sheet of white gelatine paper, which it resembles in appearance. Round the margin of this carapace are a number of little bosses or dots, which vary in different individuals. The cilia are not disposed, as at first appeared, in two separate and distinct disks, but are continuous, as in the annexed sketch. Down each side are two long muscular bands, distinctly striated, and when they contract, the ciliary apparatus is drawn in. As this contraction takes place, two apparently elastic bands, to which the ciliary lobes are attached, are bent downwards, till they look like the C springs behind a gentleman's carriage; and they regain their former position of slight curvature, when the cilia are again thrust out.
Pterodina patina—tail-foot.
The gizzard is three-lobed, and curiously grasped by forked expansions of the handles of the hammers. The tail, or tail-foot, can be withdrawn or thrust out at the will of the creature; and when in a good position for observation, a slight additional pressure will keep it so for examination. Delicate muscular longitudinal bands, forked towards the end of their course, supply the means of performing some of its motions, and one, or perhaps two, spiral threads extend through the upper half of its length, and either act as muscles, or as elastic springs for its extension. The intestines and other viscera are clearly exhibited, and a strong ciliary action conducts the food to the gizzard-mouth.
To return to the tail. One spiral fibre is easily discovered; but I have often, and at an interval of months, seen the appearance of two, and am in some doubt whether this was a deception, arising from the compression employed, or was a genuine indication.
A. Metopidia acuminata, as drawn by Mr. Gosse. B. Specimen as seen and described in text. c. Mouth or gizzard.
Where this Rotifer occurs I have usually found it plentiful, but unfortunately could obtain no constant supplies after I had determined to make a special study of the remarkable tail, which is much more complicated than I have described. The Pterodina lived for some time in captivity, and for a week or two I could obtain them from my glass tank. They were likewise to be found for some weeks in the same part of the pond, but not all over it, until one day not a single specimen could be discovered, notwithstanding a persevering search nor was I afterwards able to get any from that pond during the remainder of the year.
Trichodina pediculus.
Several other Rotifers, with and without carapaces, were among the same mass of confervæ, among them a Metopidia, with a firm shell, a forked jointed tail, and a projection in front which worked like a pickaxe among the decaying weed. There were likewise specimens of the long-necked animalcules (Trachelii), groups of Vorticella, some specimens of Volvox, and a small Trichodina pediculus, which, when magnified two hundred and sixty linear, was about the size of a sixpence and equally round. The edge was beautifully fringed with a circle of cilia; in an inner circle was a row of locomotive organs, and the centre exhibited vacuoles constantly opening and shutting. This creature, as before explained, is often found as a parasite upon the polyps. On one occasion a glimpse was caught of a Rotifer similar in shape to the common wheel animalcule, but with a yellow inside. Possibly it was the object so beautifully delineated by Mr. Gosse, in his "Tenby," and described as the "Yellow Philodine," but this must remain in doubt, as it managed to escape before it could be secured.
A. Cothurnia imberbis—('Micrograph. Dict.') B and C. The specimens described in text. The figures give the linear magnification.
By the 18th of the month the Vorticellids were much more plentiful, and their changes easily watched; many left their stalks while under the microscope, after which some rushed about like animated and demented hats, others twirled round like tee-to-tums, while others took a rest before commencing their wild career. But the common Vorticellæ were not the only or the most interesting representations of their charming order, for upon some threads of conferva were descried several elegant crystal vases standing upon short foot-stalks, and containing little creatures that jumped up and down like "Jack in the box." These were so minute, that a power of four hundred and thirty linear was advantageously brought to bear upon them. When elongated their bodies were somewhat pear-shaped, but more slender, and variegated with vacuoles and particles of food. The mouths resembled those of Vorticellæ, and put forth circles of vibrating cilia. They were easily alarmed, when the cilia were retracted, and down they sank to the bottom of their vases, quickly to rise again. In one bottle there were two living in friendly juxtaposition. This was not a case of matrimonial felicity, nor of Siamese twins, but of fission, or reproduction by division. The original inhabitant of the tube finding himself too fat, or impelled by causes we do not understand, quietly divided himself in two, and as the house was big enough, no enlargement was required. How many stout puffy gentlemen must envy this process; how convenient to have two thin lively specimens of humanity made out of one too obese for locomotion. Man is, however, sometimes the victim of his superior organization, and no process of "fission" can make the lusty lean.[9]
[9] Balbiani in his 'Recherches sur les Phénomènes Sexuels des Infusoires,' speaks of the Vorticellids as the only Infusoria dividing longitudinally. In other species such appearances arise from conjunction.
The bottles in which these creatures live, in happy ignorance that they are called by so crackjaw a name as Cothurnia imberbis, were described as Carapaces by Ehrenberg, but they bear no resemblance to the shell of a turtle or crab. They are thrown off by the animals who preserve no other connection with them than the attachment at the bottom.
The Micrographic Dictionary describes the family Ophrydina as corresponding to Vorticellina with a carapace. Stein places them with Vorticellids, &c., amongst his Peritricha, which are characterised by a spiral wreath of cilia round the mouth.
Towards the end of the month a great number of black pear-shaped bodies (Stentor niger), visible to the naked eye, were conspicuous in some water from the Kentish Town ponds. Upon examination they were found to be filled with granules that were red by reflected, and purple by transmitted light. Each one had a spiral wreath of cilia, with a mouth situated like those of the stentors, hereafter to be described, but none of them became stationary, and in a few days they all disappeared. Stein divides Ehrenberg's Stentor igneus from S. niger; the creature described seems to have agreed with Stein's igneus, which he describes as having blood-red lilac, cinnabar, or brown-red pigment particles, and as much smaller than his S. niger. In the same water were specimens of that singular Rotifer, the Salpina, about 1—150" long, and furnished with a lorica, or carapace, resembling a three-sided glass box, closed below, and slightly open along the back. At the top of this box were four, and at the bottom three, points or horns, and the creature had one eye and a forked tail. Keeping him company was another little Rotifer, named after its appearance, Monocerca rattus, the 'One-tailed Rat.' This little animal had green matter in its stomach, which was in constant commotion. I ought to have observed that the Salpina repeatedly thrust out its gizzard, and used it as an external mouth. In the annexed sketch the Salpina is seen in a position that displays the dorsal opening of the carapace. Its three-cornered shape is only shown by a side view.
Here we close a brief account of what March winds brought in their train. The next chapter will show the good fortune that attended April showers.
Salpina redunca.
CHAPTER V.
APRIL.
The beautiful Floscule—Mode of seeking for Tubicolor Rotifers—Mode of illuminating the Floscule—Difficulty of seeing the transparent tube—Protrusion of long hairs—Lobes—Gizzard—Hairy lobes of Floscule not rotatory organs—Glass troughs—Their construction and use—Movement of globules in lobes of Floscule—Chætonotus larus—Its mode of swimming—Coleps hirtus—Devourer of dead Entomostraca—Dead Rotifer and Vibriones—Theories of fermentation and putrefaction—Euplotes and Stylonichia—Fecundity of Stylonichia.
EW living creatures deserve so well the appellation of "beautiful" as the Floscularia ornata, or Beautiful Floscule, although to contemplate a motionless and uncoloured portrait, one would imagine that it exhibited no graces of either colour or form. Mr. Gosse has, however, done it justice, and the drawing in his "Tenby" is executed with that rare combination of scientific accuracy and artistic skill, for which the productions of his pencil are renowned.
The Beautiful Floscule. A.—Partially protruded. B.—Freely protruded, with three eggs. C.—Appearance of young. D.—Floscule seventeen hours old. D'.—Jaws of Floscule, as figured by Mr. Gosse.
Probably the sketches in several works of authority representing the long cilia as short bristles, are merely copies from old drawings, from objects imperfectly seen under indifferent microscopes, and before the refinements of illumination were understood. Be this as it may, any reader will be fortunate if on an April, or any other morning, he or she effects the capture of one of these exquisite objects, although the first impression may not equal previous expectations, as the delicacy of the organism is not disclosed by a mode of using the light which answers well enough for the common infusoria.
When the Floscules, or other tubicolar Rotifers are specially sought for, the best way is to proceed to a pond where slender-leaved water-plants grow, and to examine a few branches at a time in a phial of water with a pocket-lens. They are all large enough to be discerned, if present, in this manner, and as soon as one is found, others may be expected, either in the same or in adjacent parts of the pond, for they are gregarious in their habits. With many, however, the first finding of a Floscule will be an accident, as was the case last April, when a small piece of myriophyllum was placed in the live-box, and looked over to see what it might contain. The first glimpse revealed an egg-shaped object, of a brownish tint, stretching itself upon a stalk, and showing some symptoms of hairs or cilia at its head. This was enough to indicate the nature of the creature, and to show the necessity for a careful management of the light, which being adjusted obliquely, gave quite a new character to the scene. The dirty brown hue disappeared, and was replaced by brilliant colours; while the hairs, instead of appearing few and short, were found to be extremely numerous, very long, and glistening like delicate threads of spun glass.
Knowing that the Floscules live in transparent gelatinous tubes, such an object was carefully looked for, but in this instance, as is not uncommon, it was perfectly free from extraneous matter, and possessed nearly the same refractive power as the water, so that displaying it to advantage required some little trouble in the way of careful focusing, and many experiments as to the best angle at which the mirror should be turned to direct the light. When all was accomplished, it was seen that the Floscule had her abode in a clear transparent cylinder, like a thin confectioner's jar, which she did not touch except at the bottom, to which her foot was attached. Lying aside her in the bottle were three large eggs, and the slightest shock given to the table, induced her to draw back in evident alarm. Immediately afterwards she slowly protruded a dense bunch of the fine long hairs, which quivered in the light, and shone with a delicate bluish-green lustre, here and there varied by opaline tints.
The hairs were thrust out in a mass, somewhat after the mode in which the old-fashioned telescope hearth-brooms were made to put forth their bristles. As soon as they were completely everted, together with the upper portion of the Floscule, six lobes gradually separated, causing the hairs to fall on all sides in a graceful shower, and when the process was complete, they remained perfectly motionless, in six hollow fan-shaped tufts, one being attached to each lobe. Some internal ciliary action, quite distinct from the hairs, and which has never been precisely understood, caused gentle currents to flow towards the mouth in the middle of the lobes, and from the motion of the gizzard, imperfectly seen through the integument, and from the rapid filling of the stomach with particles of all hues, it was plain that captivity had not destroyed the Floscule's appetite, and that the drop of water in the live-box contained a good supply of food.
Sometimes the particles swallowed were too small to be discerned, although their aggregate effect was visible; but often a monad or larger object was ingulfed, but without any ciliary action being visible to account for the journey they were evidently compelled to perform. The long hairs took no part whatever in the foraging process, and as they do not either provide victuals or minister to locomotion, they are clearly not, as was supposed by early observers, representatives of the "wheels," which the ordinary Rotifers present. Neither can the cylindrical jar or bottle be justly deemed to occupy the position of the lorica, or carapace which we have before described. The general structure of the creature and the nature of its gizzard distinctly marked it out as a member of the family we call "Rotifers," but the absence of anything like "wheels" proves that those organs are not essential characteristics of this class.
Noticeable currents are not always produced when the mouth of this Floscule is fully expanded. On one occasion, one having five lobes was discovered standing at such an angle in a glass trough that the aperture could be looked down into. The position rendered it impossible to use a higher power than about two hundred linear, but with this, and the employment of carmine, nothing like a vortex was seen during a whole evening, although a less power was sufficient to show the ciliary whirlpools made by small specimens of Epistylis and Vaginicola, which were in the small vessel. The density of the integument was unfavorable to viewing the action of the gizzard, but it could be indistinctly perceived. The contractions and subsequent expansions of the cup, formed by the upper part of the creature, may be one way in which its food is drawn in, but there is no doubt it can produce currents when it thinks proper. Sometimes animalcules in the vicinity of Floscules whirl about as if under the influence of such currents. Some may be seen to enter the space between the lobes, swim about inside, and then get out again, while every now and then one will be sucked in too far for retreat.
Above the gizzard in the Horned Floscule,[10] I have seen an appearance as if a membrane or curtain was waving to and fro, while another was kept in a fixed perpendicular position. Mr. Gosse, speaking of this genus, observes "that the whole of the upper part of the body is lined with a sensitive, contractile, partially opaque membrane, which a little below the disk recedes from the walls of the body, and forms a diaphragm, with a highly contractile and versatile central orifice. At some distance lower down another diaphragm occurs, and the ample chamber thus enclosed forms a kind of crop, or receptacle for the captured prey."
[10] The Horned Floscules (F. cornuta) which I have found, and which bred in a glass jar, were not so large as those described by Mr. Dobie, as quoted in 'Pritchard's Infusoria.' Mr. Dobie's specimens were 1—40" when extended; mine about half that size, five-lobed, and with a long slender proboscis, standing in a wavy line outside one lobe. Mr. Dobie also describes an F. campanulata, with five flattened lobes. The 'Micrographic Dictionary' pronounces these two species "doubtfully distinct." I have three or four times met with a variety of F. ornata, in which one lobe was much enlarged and flattened, but they had no proboscis. In what I take for F. cornuta, the horn or proboscis has sometimes been a conspicuous object, and at others so fine and transparent as to be only visible in certain lights.
"From the ventral side of the ample crop that precedes the stomach, there springs in F. ornata a perpendicular membrane or veil, partly extending across the cavity. This is free, except at the vertical edge, by which it is attached to the side of the chamber, and being ample and of great delicacy, it continually floats and waves from side to side. At the bottom of this veil, but on the dorsal side, are placed the jaws, consisting of a pair of curved, unjointed, but free mallei, with a membranous process beneath each."
The Beautiful Floscule could always be made to repeat the process of retreating into her den, and coming out again to spread her elegant plumes before our eyes, by giving the table a smart knock, and her colours and structure were well exhibited by the dark-ground illumination, which has been explained in a previous page.
An object like this should be watched at intervals for hours and even days, especially if the eggs are nearly ready to give up their infantile contents. This was the case with the specimen described, and after a few hours a young Floscule escaped, looking very much like a clumsy little grub. After a few awkward wriggles the new-born baby became more quiet, and on looking at it again at the expiration of seventeen hours, it had developed into the shape of a miniature plum-pudding, with five or six tiny lobes expanding their tufts of slender hair. Unfortunately its further proceedings were not seen, or it would have been interesting to note the growth of the foot, and the formation of the gelatinous tube, which is probably thrown off in rings.
To view the details of the structure of a Floscule, it must be placed in a live-box or compressorium, and if specimens are scarce, they should not be allowed to remain in the limited quantity of water those contrivances hold, after the observations are concluded, but should be carefully removed, and placed in a little vial, such as homœopathists use for their medicine. By such means an individual may be kept alive for many days. It is also interesting to place a little branch of the plant occupied by Floscules or similar creatures, in a glass trough, where they may be made quite at home, and their proceedings agreeably watched by a one-inch or two-thirds power. These troughs,[11] which can be obtained of the optician, should be of plate glass, about three inches long, nearly the same height, and about half an inch wide. If narrower, or much taller, they will not stand, which is a great inconvenience. The pieces of glass are stuck together with marine glue, and a very simple contrivance enables the plants or other objects to be pressed near the front, and thus brought into better view. A strip of glass, rather narrower than the width of the trough, is dropped into it, and allowed to fall to the bottom. Then a piece of glass rather shorter than the trough, and rather higher than its front side, is placed so as to slope from the front of the bottom towards the back at the top. The piece of glass first dropped in keeps it in the right position, and the trough is thus made into a V-shaped vessel, wide at the top and gradually narrowing. Any object then placed in it will fall till it fits some part of the V, where it will remain for observation. A small wedge of cork enables the moveable piece of glass to be thrown forwards, until it assumes any angle, or is brought parallel to the front of the trough.
[11] The shallow cells with thin sliding covers devised by Mr. Curteis (of Baker's), are still more convenient when no pressure is required, and the objects are small. When not under the microscope they can be kept full of water by immersion in a tumbler.
A power of five or six hundred diameters generally enables a movement of small globules to be seen at the extremity of the lobes of the Floscule, and the gizzard may be made plain by dissolving the rest of the creature in a drop of solution of caustic potash. It also becomes more visible as the supply of food falls short. Mr. Gosse describes the body as "lined with a yellowish vascular membrane," and young specimens exhibit two red eyes, which may or may not be found in adults. When these eyes of Rotifers are not readily conspicuous, they must be sought for by opaque illumination, or by the dark-ground method which, especially with the parabola, is successful in bringing them out.
Naturalists, and possibly the specimens also, do not always agree in the number of lobes assigned to the "Beautiful Floscule," and although it is easy enough to count them in some positions, the observer may have to exercise a good deal of patience before he is certain whether they are five or six. For a long evening only five could be discerned in the specimen now described, but the next night six were apparent without difficulty or doubt. The hairs also will not appear anything like their true length or number, unless the object-glass is good, and great care is taken not to obscure them by a blaze of ill-directed light.
Chætonotus larus (swimming).
After the Floscules had been sufficiently admired and put aside, for observations to be repeated on future occasions, a Rotifer attracted attention by his merry-andrew pranks, throwing himself in all directions by means of two long and extremely mobile toes attached to his tail-foot. Then came a creature swimming like an otter, thrusting his head about on all sides, and looking much more intelligent than most of his compeers of the pond. Looked at vertically, he was somewhat slipper-shaped, the rounded heel forming his head, then narrowing to a waist, and expanding towards the other end, which projected in a fork. All round him were long cilia, which were conspicuous near the head, and a fine line indicated the passage from his mouth to the stomach, which seemed full of granular matter. Presently he took to crawling, or rather running, over a thread of conferva, and then his back was elegantly arched, and his cilia stood erect like the quills of a porcupine. This was the Chætonotus larus.
Chætonotus larus (crawling).
In Pritchard's "Infusoria," the views of those writers are followed who rank this animal amongst the Rotifers, and place it in the family Icthidina. To help out this theory, the cilia upon the ventral surface are imagined to form a "band-like rotary organ;" but in truth they bear no resemblance whatever to the so-called wheels of the ordinary Rotifers, nor is there anything like the gizzard which true Rotifers present. Ehrenberg treated it as a Rotifer, and Dujardin placed it among the Infusoria, in a particular class, comprehending symmetrical organisms. The 'Microscopic Dictionary' remarks that its "structure requires further investigation,"[12] and while the learned decide all the intricate questions of its zoological rank, the ordinary observer will be pleased to watch its singular aspect and lively motions. Its size, according to the 'Micrographic Dictionary,' varies from 1—710" to 1—220", and while its general proceeding may be watched with an inch or two-thirds object-glass, and the second eye-piece, a power of five hundred linear (obtained by a quarter or a fifth) is required to make out the details of its structure. If placed in a live-box with threads of conferva, and a little decayed vegetation, it may be observed to group about among them, and shake them like a dog.
[12] See a valuable paper by Mr. Gosse, "History of the Hairy-backed Animalcules," 'Intellectual Observer,' vol. v, p. 387, in which the known species are described and reasons given for following Vogt and ranging them with the Turbellarian worms.
We have said that water-fleas were among the inhabitants of a bottle filled at the pond, and as they go the way of all flesh, it is common to find some odd-looking animalcules ready to devour their mortal remains. These are creatures shaped like beer-barrels, upon short legs, and which swim with a tubby rolling gait. Looking at one of these little tubs lengthwise, a number of lines are seen, as though the edge of each stave projected a little above the general level, and transverse markings are also apparent, which may be compared to hoops. This is the Coleps hirtus, which differs from the usual type of Infusoria, by being symmetrical, that is, divisible into two equal and similar halves. The dimensions of this species vary from 1—570 to 1—430, and its colour varies from white to brown. It has been observed to increase by transverse self-division, and has two orifices, one at each end, for receiving food and ejecting the remains. It often requires some little trouble to get a good view of the cilia, which are arranged in transverse and longitudinal rows. A power of one hundred and fifty linear is convenient for viewing it in motion, but when quiet under pressure, one of five or six hundred may be used with advantage.
Coleps hirtus.
Among the rubbish at the bottom of the bottle, in which the coleps was found, was a minute dead Rotifer, the flesh of which was fast disappearing, but upon being examined with a power of nine hundred and sixty diameters, it was observed to swarm with extremely minute vibriones, the largest only appearing under that immense magnification like chains of bluish-green globules, not bigger than the heads of minikin pins, while the smallest were known by a worm-like wriggling, although their structure could not be defined. These vibriones are probably members of the vegetable world, and they always appear when animal matter undergoes putrefaction.
M. Pasteur has brought forward elaborate experiments to show that the development of the yeast plant is an act correlative to alcoholic fermentation, and in like manner the growth of vibriones may stand in correlation to putrefactive decomposition.
A, Euplotes (patella); B, side view of ditto; C, stylonichia.
Ehrenberg considered them animals, and fancied he detected in them a plurality of stomachs; but the vegetable theory is the more probable, at any rate of the species under our notice, which is often seen, though not always so minute.
At this time two interesting animalcules were very plentiful—the Euplotes patella, and Stylonichia, both remarkable as exhibiting an advance in organization, which approximates them to the higher animals. In addition to cilia they possess styles, which take the place of the limbs of more elaborately-constructed creatures, and give a variety to their means of locomotion. The Euplotes is furnished with an oval carapace covering the upper surface, which in different individuals, and probably at different ages, exhibits slightly varied markings round its margin, which in the specimen drawn above consisted of dots. They can run, climb, or swim, and exemplify a singular habit which several of the infusoria possess, that of moving for a little time in one direction, and then suddenly, and without any apparent cause, reversing it. If the reader is fond of learned appellations, he can call this diastrophy, but we do not know that he will be any the wiser for it.
The Stylonichia are oval animalcules, surrounded by cilia, and having moreover a collection of styles, both straight and curved, the latter called uncini, or little hooks. They swim steadily on, and then dart back, but not so far as they have advanced, and may be seen to keep up this fidgety motion by the hour together. Pritchard tells us Ehrenberg found that a single animalcule lived nine days; during the first twenty-four hours it was developed by transverse self-division into three animals; these in twenty-four hours formed two each in the same manner, so that by self-division only (without ova), these animalcules increased three or four-fold in twenty-four hours, and may thus produce a million from a single animalcule in ten days. Such are the amazing powers of reproduction conferred upon these humble creatures, powers which are fully employed when the surrounding circumstances are favorable, and which, in the aggregate, change the condition of large masses of matter, and bring within the circle of life millions upon millions of particles every minute of the day.
CHAPTER VI.
MAY.
Floscularia cornuta—Euchlanis triquetra—Melicerta ringens—its powers as brickmaker, architect, and mason—Mode of viewing the Melicerta—Use of glass-cell—Habits of Melicerta—Curious Attitudes—Leave their tubes at death—Carchesium—Epistylis—Their elegant tree forms—A Parasitic Epistylis like the "Old Man of the Sea"—Halteria and its Leaps—Aspidisca Lynceus.
AY, the first of summer months, and of old famous for floral games, which found their latest patrons in the chimney-sweeps of London, is a good time for the microscopist among the ponds, for the increase of warmth and heat favours both animal and vegetable life, and so we found as we carried home some tops of myriophyllum, and soon discovered a colony of tubicolor rotifers among the tiny branches. They proved to be Floscules, generally resembling the F. ornata, described in a previous page, but having a long slender proboscis hanging like a loose ringlet down one side. The cilia or hairs were not so long as in the Beautiful Floscules we had before obtained, nor was their manner of opening so elegant; but they were, nevertheless, objects of great interest, and were probably specimens of the Floscularia cornuta. A swimming rotifer in a carapace somewhat fiddle-shaped, with one eye in its forehead, and a two-pronged tail sticking out behind (the Euchlanis triquetra), also served to occupy attention; but a further search among the myriophyllum revealed more treasures of the tube-dwelling kind. These were specimens of that highly curious Rotifer, the Melicerta ringens, who, not content with dwelling, like the Floscules, in a gelatinous bottle, is at once brickmaker, mason, and architect, and fabricates as pretty a tower as it is easy to conceive. The creature itself stands upon a retractile foot-stalk, and thrusts out above its battlements a large head, with four leaf-like expansions surrounded by cilia. Between the lower lobes, or leaves, the gizzard is seen grinding away, and above it is an organ, not always displayed, and of which Mr. Gosse was fortunate enough to discover the use. This eminent naturalist likens it to the circular ventilator sometimes inserted in windows, and he found it was the machine for making the yellow ornamental bricks of which the tower is composed. Pellet by pellet, or brick by brick, does the Melicerta build her house, which widens gradually from the foundation to the summit, and every layer is placed with admirable regularity.
In order to obtain the materials for her brickmaking the Melicerta must have the power of modifying the direction of the ciliary currents, so as to throw a stream of small particles into the mould, which is a muscular organ, and capable of secreting a waterproof cement, by which they are fastened together. The result is, not to produce anything like the tubes made by the caddis-worms out of grains of sand, but entirely to change the appearance of the materials employed. All large particles are rejected, and only those retained which will form a homogeneous pulp with the viscid secretion; and when the process is complete the head of the creature is bent down, and the pellet deposited in its appropriate place. Each pellet appears originally to possess a more or less conical figure, but when they are squeezed together to make a compact wall they all tend to a hexagonal form, by which they are able to touch at all points, and any holes or interstices are avoided.
According to Professor Williamson the young Melicerta commences her house by secreting "a thin hyaline cylinder," and the first row of pellets are deposited, not at the base as would be expected, but in a ring about the middle of the tube. "At first new additions are made to both extremities of the enlarging ring; but the jerking constrictions of the animal at length force the caudal end of the cylinder down upon the leaf, to which it becomes securely cemented by the same viscous secretion as causes the little spheres to cohere."
Round the margins of the lobes or expansions may be seen delicate threads towards which others radiate; these are thought by Mr. Gosse to be portions of a nervous system, and two calcars or feelers serve as organs of relation. The young Melicertas are likewise furnished with a pair of eyes, which are probably rudimentary, and disappear as they grow up.
The Melicerta tubes, being large enough to be visible to the naked eye, are easily crushed in the live-box, and to avoid this, they are conveniently viewed in a shallow glass cell, covered up as before described. By occasionally changing the water one may be kept for days in the same cell, and will reward the pains by frequently exposing its flower-like head. Usually the horns or feelers come out first, and then a lump of flesh. After this, if all seems right, the wheels appear, and make a fine whirlpool, as may be readily seen by the use of a little indigo or carmine.
The Melicerta is, however, an awkward object to undertake to show to our friends, for as they knock at the door she is apt to turn sulky, and when once in this mood it is impossible to say when her fair form will reappear. At times the head is wagged about in all directions with considerable vehemence, playing singular antics, and distorting her lobes so as to exhibit a Punch and Judy profile. When these creatures die they leave their tubes, which are often found empty in the ponds they frequent. The Melicertas are conveniently viewed with a power of from sixty to one hundred linear, and a colony of them may be kept alive for some weeks in a glass jar or tank.
Among the remainder of my tiny captives were two beautiful members of the Vorticella family, Epistylis and Carchesium. The reader will remember that in the Vorticella previously described, the bells stood upon stalks that were very flexible, and retractile by means of a muscle running down their length. The Epistylis is, as its name imports, the dweller on a pillar. The stem is stiff, or only slightly flexible, and has no apparatus by which it can be drawn down. The specimen mentioned stood like a palm-tree, and the large oval bells drooped elegantly on all sides, as its portrait will show. At times they nodded with a rapid jerk.
Epistylis.
The Carchesium differs from the common Vorticella, by branching like a tree, but the stems are all retractile, although the trunk seldom exercises the power. A group of these creatures presents a spectacle of extraordinary beauty—it looks like a tree from fairy-land, in which every leaf has a sentient life. In general structure the bells of the Epistylis and the Carchesium resemble the common Vorticella, and like them may be seen with a power of about one hundred linear for general effect, and with a higher one for the examination of special points. Pritchard notices three species of Carchesium, and eighteen of Epistylis;[13] some of which it is to be hoped will turn out to be only varieties.
[13] An interesting Epistylis, called Digitalis, from its bells resembling fox-glove flowers in shape, occurs as a parasite upon the Cyclops quadricornis, a very common entomostracan in fresh-water ponds. At this moment I have a beautiful specimen, branching like a bushy tree, and attached to the tail of a Cyclops, who can scarcely move under his burden, which is like Sinbad's "Old Man of the Sea." (See illustration [above].)
Towards the end of this month rotifers abounded, and polyps were plentiful. Among the rotifers was one about a two-hundredth of an inch long, protected by a carapace, and having a tail terminating in a single style, hence called "Monostyle." There is perhaps no class of creatures that present so many curious and unexpected forms as the rotifers; and although we have noticed a good many, there are far more that remain to be found and described.
The water in which the preceding animals dwelt was enlivened by the jumps of the Halteria, a little globe surrounded by long fine cilia, with which its movements were effected; and its companion was the Aspidisca lynceus, an oval animalcule, having a distinct cilia or lorica, and furnished, in addition to cilia, with bristles, which enable it to walk and climb as well as swim.
There were also some eggs of rotifers attached to the water plants, in which motion could be descried at intervals, and a little red eye observed. These eggs are always large in proportion to the creatures that lay them, and if they escape being devoured by enemies, may be watched until their contents step forth.
In this, as in other months, omission is made of creatures that have already come under notice, or our list would assume larger dimensions.
CHAPTER VII.
JUNE AND JULY.
Lindia Torulosa—Œcistes Crystallinus—A professor of deportment on stilts—Philodina—Changes of form and habits—Structure of Gizzard in Philodina family—Mr. Gosse's description—Motions of Rotifers—Indications of a will—Remarks on the motions of lower creatures—Various theories—Possibility of reason—Reflex actions Brain of insects—Consensual actions—Applications of physiological reasoning to the movements of Rotifers and Animalcules.
PRESSURE of other occupations prevented full use being made of June and July, nor was the weather at all propitious. For this reason the microscopic doings of these two months are recorded in one chapter.
As usual the Kentish Town ponds were productive of objects, and among them were several rotifers not found in the previous months. The first of these was a very small worm-like thing, with one eye, a tuft of cilia about the mouth, and two toes at the tail end. Had it not been for the jaws, which were working like fingers thrust against each other, and which were unmistakably of the rotifer pattern, the animal might have been supposed to belong to some other class. According to the 'Micrographic Dictionary,' the Lindia torulosa is 1—75" long, but this specimen was only about 1—200". It was possibly very young, and did not thrust out its cilia in two distinct tufts, as Cohn describes, although it may have had the power of doing so. At times it sprang quickly backwards and forwards, bringing its head where its tail was before. This object required for its comfortable elucidation a power of about six hundred linear.
Œcistes crystallinus.
Among the common water-plants, which are worth examining as the probable abodes of rotifers or infusoria, is the pretty little thing called "star-weed," some of which was obtained from the last-mentioned ponds, and on examination yielded a specimen of a tube-dwelling rotifer, the Œcistes crystallinus, which, although less beautiful than the Floscules or the Melicerta, is, nevertheless, a pretty and interesting object. In this instance a little rough dirty tube, about 1—70" long, was observed to contain an animal capable of rising up and expanding a round mouth garnished with a wreath of cilia; while a little below, the indefatigable and characteristic gizzard of the tribe was in full play. A power of two hundred and forty linear sufficed to afford a good view, and it was seen that a long, irregular, conical body was supported upon a short wrinkled stalk. The usual drawings represent this creature with a short bell-shaped body upon a very long slender pedicle. Possibly this one might have been able to show himself under this guise, but he did not attempt it; his appearance being always pretty much as described, which made the foot shorter and the body longer than the measurements which naturalists have given, and according to which the whole creature is 1—36" long, although the body is only 1—140". The tube of the Œcistes is called a "lorica," or carapace; but it has in truth no right whatever to the appellation.
Another strange rotifer, of whose name I am uncertain, had an ovalish oblong body, and a pair of legs like compasses, twice as long as himself. His antics were those of a posture-master, or "Professor of Deportment" on stilts. Sometimes he stood bolt upright, bringing his legs close together; then they were jauntily crossed, and the body carried horizontally; then the two legs would be slightly opened, and the body thrown exactly at right-angles to them. These antics were repeated all the while the observation lasted, and had a very funny effect in proving that drollery is practised, if not understood, in the rotatorial world.
Philodina (swimming).
Another kind of rotifer was abundant—the Philodina, which belongs to the same family as the common wheel-bearer, namely, the Philodinæa. The Philodina is a good deal like the common wheel-bearer, or Rotifer vulgaris, but is usually of a stouter build, and carries his eyes in a different place. In the common rotifer these organs are situated on the proboscis, while those of the Philodina are lower, and said to be "cervical." The changes of form in this rotifer are still more remarkable than in the common wheel-bearer. When resting it resembles a pear-shaped purse, puckered in at the mouth. Then it thrusts out its tail-foot, swells its body to an oval globe, protrudes its feeler, and slightly exposes a row of cilia. After this two distinct wheels are everted, and as their cilia whirl and spin, the animal is swiftly rowed along, until it thinks proper to moor itself fast by the tail-foot, and employ all its ciliary power in causing currents to converge towards its throat. When it pleases it can elongate the body, till it becomes vermiform, and it walks like the common rotifer, by curving its back, and bringing its nose and its tail in contact with the ground.
Philodina (crawling).
The gizzard of this family (Philodinæa) presents a considerable deviation from the perfect form exhibited by the Brachions. According to Mr. Gosse, "The mallei and the incus (terms already explained) are soldered together into two subquadrantic-globular masses, which appear to be muscular, but invested with a solid integument. The manubria (handles) may still be recognised in a vertical aspect as three loops, of which the central one is chiefly developed, and in a vertical aspect as a translucent reniform (kidney-shaped) globe." These descriptions are not easy to understand, not from any want of clearness or precision in the words employed, but from the complicated character of the organ, and its very different appearance under different aspects. To make the matter more intelligible, Mr. Gosse adds, "the structure and action of an apparatus of this type may be made more clear by a homely illustration. Suppose an apple to be divided longitudinally, leaving the stalk attached to one half. Let this now be split again longitudinally so far as the stalk, but not actually separating either portion from it. Draw the two portions slightly apart, and lay them down on their rounded surfaces. They now represent the quadrantic masses in repose, the stalk being the fulcrum, and the upper surfaces being crossed by the teeth. By the contraction of the muscles, of which they are composed, the two segments are made to turn upon their long axis, until the points of the teeth are brought into contact, and the toothed surfaces rise and approach each other. The lower edges do not, however, separate as the upper edges approach, but the form of the mass alters, becoming more lenticular, so that when the toothed surfaces are brought into their closest approximation, the outline has a subcircular figure. It is on account of this change of form that I presume the masses themselves to be partially composed of muscle."
These remarks, although specially made of the Rotifer macrurus, are in the main applicable to all the Philodinas, but the student must not expect to understand any of the complicated gizzards of the rotifers without repeated observations, and no small exercise of patience. It is common to call the portions of the Philodine-pattern gizzard "stirrup-shaped," but Mr. Gosse has shown them to be quadrantic, that is, shaped like the quarter of a sphere.
As we are not very well off with subjects for description in these two months, we can afford a little time to consider a question that continually arises in the mind, on viewing the movements of animalcules, and especially of any so highly developed as the rotifers, namely, to what extent motions which appear intelligent are really the result of anything like a conscious purpose or will. When any of the lower animals—a bee, for example—acts in precisely the same way as all bees have acted since their proceedings have been observed, we settle the question by the use of the term instinct. Those who take the lowest view of insect life, assume that the bee flies because it has wings, but without wishing to use them, and that the nerves exciting them to action are in their turn excited, not by volition, but by some physical stimulus.
The sight or the smell of flowers is thought by the same reasoners to be capable of attracting the insect, which is unconscious of the attraction, while proximity of food stimulates the tongue to make the movements needful for its acquisition, and so forth. The cells, they tell us, are built according to a pattern which the earliest bee was impelled to construct by forces that bear no analogy to human reason and human will, and so originate all the ordinary processes of bee life. Sometimes, however, it happens that man or accident interposes particular obstacles, and forthwith there appears a particular modification of the orthodox plan, calculated to meet the special difficulty. How is this? Does any one of the difficulties which the bee or the ant is able to get over, produce precisely that kind of electrical disturbance, or polar arrangement of nerve particles that is necessary to stimulate the first step of the action by which the difficulty is surmounted; and does the new condition thus established stimulate the second step, and so forth, or can the bee, within certain limits, really think, design, and contrive?
No questions are more difficult of solution; but while protesting against a tendency to undervalue all life below that of man, we must remember we have in our bodies processes going on which are not the result of volition, as when the blood circulates, and its particles arrange themselves in the pattern required to form our tissues and organs, and also that many of our actions belong to the class termed by physiologists, "reflex," that is, the result of external impressions upon the nervous system, in which the sentient brain takes no part. Thus when a strong light stimulates the optic nerve, the portion of brain with which it is connected in its turn stimulates the iris to contract the pupil; and it is supposed that after a man has begun to walk, through the exercise of his will, he may continue to walk, by a reflex action; as his feet press the ground they transmit an impression to the spinal cord, and the legs receive a fresh impulse to locomotion, although the mind is completely occupied with other business, and pays no attention to their proceedings.[14] The ordinary movements of insects appear to be of this character, and to be excited by the ganglia belonging to the segment to which the moving limbs are attached. Thus a centipede will run, after its head has been cut off, and a water-beetle (Dytiscus) swam energetically when thrown into water after its brain had been removed.[15]
[14] See Carpenter's 'Manual of Physiology.'
[15] Carpenter's 'Manual of Physiology,' p. 551.
It must not, however, be assumed that the brain of insects has nothing to do with their movements. It is probably the means of co-ordinating or directing them to a common end, and gives rise to what are called consensual movements, that is, movements which are accompanied or stimulated by a sensation, although not controlled by a will. In man these actions are frequently exhibited, "as when laughter is provoked by some ludicrous sight or sound, or by the remembrance of such at an unseasonable hour."[16] Sneezing is another instance of a sensation leading to certain motions, without any intervention of the human will.
[16] Ibid., p. 543.
Speaking of these consensual motions, Dr. Carpenter observes, "It is probable, from the strong manifestations of emotion, exhibited by many of the lower animals, that some of the actions which we assemble under the general designation of instinctive are to be referred to this group."
The insect brain is composed of a supra-œsophagal ganglion and infra-œsophagal one. Von Siebold says, the first corresponds to the cerebrum of the vertebrata, and "the second is comparable, perhaps, to the cerebellum or spinal cord."[17] The superior ganglion gives off nerves to the antennæ and eyes, the lower one to the mandibles, &c. So far as is known the insects that exhibit the most intelligence have the largest and best developed brains.
[17] 'Anatomy of Invertebrates,' Burnett's trans.
A special volume would be required for anything like a complete examination of the little which is known on this subject, but these few remarks may assist the microscopic beginner in examining the movements of his subjects, and guard against the error of referring to reason and volition those which are, probably, either the direct result of stimulants applied to the surface (as in nerveless creatures), or the indirect (reflex) result of such stimulants in beings like the rotifers, who have a nervous system; or the result of sensations, which excite actions without previously referring the matter to the decision of a will. It must not, however, be too readily assumed that the behaviour of creatures possessing distinct organs is entirely automatic; and we must not forget that even the best physiologists know very little concerning the range of functions which the nervous ganglia of the invertebrata are able to discharge.
CHAPTER VIII.
AUGUST.
Mud coloured by worms—Their retreat at alarm—A country duck-pond—Contents of its scum—Cryptomonads—Their means of locomotion—A Triarthra (three-limbed Rotifer)—The Brachion or Pitcher Rotifer—Its striking form—Enormous gizzard—Ciliary motion inside this creature—Large eye and brain—Powerful tail—Its functions—Eggs.
