The Euglena, a very extensive genus of Infusoria, have smooth bodies and green particles imbedded in the sarcode, which fills their interior; and M. Wöhler discovered that the green mantle covering the saline springs at Rodenberg and Königsborner, which consists of three species of these green Infusoria, gives out bubbles of pure oxygen; thus indicating a respiratory process in these animals, the same with that in plants, namely, fixing the carbonic acid of the atmosphere and exhaling oxygen, a singularly close analogy, if not identity, of action. The Euglenæ are also distinguished by an irregular oblong space in the head filled with a red liquid; but, as it does not contain a crystalline lens, it can only be regarded as the very earliest rudiment of an eye, totally incapable of distinguishing objects, though probably sensible to the influence of light. They swim with a smooth gliding and often rotatory motion, producing a kind of flickering on the surface of the water by the lashing of a long filament attached in front, and supposed to be their only organ of locomotion; nevertheless, Mr. Gosse thinks that they are covered with most minute cilia from their manner of swimming. The Euglena acus is one of the prettiest of these little animals; it is long and slender, of a sparkling green with colourless extremities, a thread-like proboscis, and a rich crimson spot. When it swims it rotates, and a series of clear, oblong bodies are seen towards the head, and another at the tail, as if they were imbedded in the flesh round a hollow.
The Loxades bursaria, which is a giant among its fellows, has an ovoid body with green particles imbedded in its interior. The outer skin is spirally grooved, so as to form a kind of network, the elevated points of which support the cilia with which its body is beset. It has a mouth and gullet lined with cilia, which force the food in balls into the soft matter in the interior, where both the food and the green particles circulate, being carried along by a gyration of the gelatinous matter in which they are imbedded.
A species of Peridinium, which is luminous at night, and occasionally covers large portions of the Bay of Bengal with a scarlet coat by day, nearly approaches the character of the unicellular Algæ. Mr. J. H. Carter observed that at first, when these animalcules were in a state of transition, their nearly circular bodies were filled with translucent green matter, closely allied, if not identical with, chlorophyll, which disappeared when the animal approaches its fixed state, and a bright red took its place: the Infusoria were then visible to the naked eye, and the sea became scarlet. The scarlet state only lasts for a few days, for each of these innumerable Infusoria becomes encysted or capsuled, and either floats on the water, or sinks to the bottom and remains motionless. The Euglena sanguinea has a scarlet state analogous to that of the Peridium. It is so minute and versatile that it is difficult to ascertain its true form, which, however, seems to be a spindle shape, with a pointed and blunt round head. In general it is of a rich emerald green, with perfectly clear, colourless extremities; but it sometimes occurs of a deep red, and in such multitudes as to give the water the appearance of blood.[[19]]
Fig. 106. Noctiluca.
The Noctiluca miliaris, a luminous inhabitant of the ocean, and the most beautiful of the Infusoria, is distinguished by its comparatively gigantic size, and by its brilliant light, which makes the sea shine like streams of silver in the wake of a ship in a warm summer evening, when they come to the surface in countless multitudes. It is a globular animal like a minute soap bubble, consisting of gelatinous matter, with a firmer exterior, and being about the thirtieth of an inch in diameter, it is visible to the naked eye, when a glass in which it is swimming is held to the light. On one side of the globe there is an indentation, from whence a tail of muscular fibre springs striped with transverse rings, which aids the animal in swimming. At the root of the tail lies the mouth, bordered on one side by a hard dentile lip leading into a funnel-shaped throat, from whence a long flickering cilium is protruded, supposed to be connected with respiration. The throat leads into a large cavity in the gelatinous substance, from whence the rudiments of an alimentary canal descend. From the internal surface of the globe sarcode fibres extend through the gelatinous matter, so as to divide it into a number of irregular compartments, in which vacuoles are often seen. They give buoyancy to the animal, and enable it to rise and sink in the water, but seem to disappear when the food is digested. The sarcode fibres constantly change their form and position, and the electric light emitted by a direct exertion of nerve power, which seems to be constant to the naked eye, really consists of momentary scintillations that increase in rapidity and intensity by the dash of an oar or the motion of the waves.
The Noctiluca is propagated by spontaneous division, a line appears bisecting the globe, which becomes more and more constricted till the animal is like a dumb-bell; the slender thread separating the two parts is then broken by their efforts to get free; the two new creatures swim off in different directions, and soon assume their adult form. But in many individuals there are clear, yellow globules with a well-defined nucleus, of a rich reddish-brown, which are the germs of the animal.
Most of the Infusoria multiply by continuous bisection, like the unicellular Algæ. The division generally begins with the nucleus, and is longitudinal or across, according to the form and nature of the animal, and is accomplished with such rapidity, that, by the computation of Professor Ehrenberg, 268,000,000 of individuals might be produced from one single animalcule of the species Paramœcium in a month. The Paramœcia are reproduced too by gemmation, and, as they are male and female, they are reproduced also like the higher classes.
The Infusoria have another mode of increasing. The animalcules either draw in or lose their cilia, and consequently come to rest. The animal then assumes a more globular form, and secretes a gelatinous substance from its surface, which hardens into a case or cyst, in which its body lies unattached and breaks up into minute ciliated gemmules, which swim forth like zoospores as soon as they come into the water by the thinning away of part of the cyst. In fact the animal is resolved into its offspring, which, as soon as free, gradually acquire the parent’s form, though at first they may bear no resemblance to it. The scarlet Peridium seen by Mr. Carter in the Bay of Bengal is propagated in this manner. For the parent Peridium is broken up within its cyst into from two to four new ones, each of which when set free and grown up might undergo the same process.
The Loxades bursaria increases by three distinct methods, and sometimes by two at a time. In autumn, or the beginning of winter, six or eight germs containing granular matter and one or more hyaline nuclei are formed within the animal, each enclosed in two contractile cysts: they lie freely in the cavity of the body, and come one by one into the water through a canal ending in a protuberance in the skin. During this time the pulsations of the vesicles within the Loxades are continued, but the gyration of the green particles is suspended till all the germs are excluded and swim away, and then it is renewed as vigorously as ever. At first the young are totally unlike their parent, but by degrees acquire its form. The Loxades is also increased by division, sometimes across, sometimes longitudinally, and, in the latter case, one half is occasionally seen to contain germs which have been excluded before the other half had separated, so that the two distinct systems of propagation are simultaneous.[[20]]