Noctiluca mainly confines itself to the shallower seas, but there are related forms met with in the warmer open seas; these belong to the genus Pyrocystis ([Fig. 334]). In one variety the body is perfectly spherical and without the big flagellum or proboscis. Professor Butschli, however, regards this species as an encysted or resting phase of the commoner and better-known form.
The late Mr. Philip Gosse, F.R.S., was the first microscopist to describe the Noctiluca. After careful observation, he wrote in his “Naturalist’s Rambles” as follows:—“I had an opportunity of becoming acquainted with the minute animals to which a great portion of the luminousness of the sea is attributed. One of my large glass vases of sea-water I had observed to become suddenly at night, when tapped with the finger, studded with minute but brilliant sparks at various points on the surface of the water. I set the jar in the window, and was not long in discovering, without the aid of a lens, a goodly number of the tiny jelly-like globules of Noctiluca miliaris swimming about in various directions. They swam with an even gliding motion, much resembling that of the Volvox globator of our fresh-water pools. They congregated in little groups, and a shake of the vessel sent them darting down from the surface. It was not easy to keep them in view when seen, owing rather to their extreme delicacy and colourless transparency than to their minuteness. They were, in fact, distinctly appreciable by the naked eye, measuring from 1⁄50th to 1⁄30th of an inch in diameter.”
Among the numerous fresh-water members of the flagellate infusoria, there is one which especially calls for notice, Codosiga, discovered by the late Professor H. J. Clark. This minute body bears a delicate funnel-shaped protoplasmic expansion or collar, common to the several members of this organic series. The flagellum is placed at the base of the oral opening, and within the circumscribed area of the collar, which is of such extreme tenuity that its true form and nature can only be determined by a very careful adjustment of the achromatic condenser and accessory apparatus employed, together with a wide-angled objective. It is seen to greater advantage by supplying the animal with very fine particles of colouring matter. In this way it is found that the infundibuliform cup consists of protoplasm, through which the flagellum is protruded and withdrawn into the general substance of the Monad’s body (Fig. 335). As many as twenty or more zooids are attached to the extremity of a slender footstalk. The length of the body, exclusive of the collar, is 1⁄2500th to the 1⁄1200th of an inch. The habitat of these bodies is fresh water. Mr. Saville Kent in 1869 discovered some of these interesting infusoria in the London Docks.
“The more exact significance of the special organ, the collar, is manifest by the circulatory currents or cyclosis induced, and there can be no room for doubt that this structure finds its precise homologue in the pseudopodia of the foraminiferous group of the Rhizopoda, in which a similar circulation or cyclosis of the constituent sarcode is exhibited. The whole of this highly-interesting flagellate order, a comparatively small one as yet, are remarkable for their pale glaucous green or florescent hue, such colour assisting materially in their recognition, even when the magnifying power employed is insufficient for the detection of the very characteristic collar with its enclosed flagellum.”[66]
Fig. 335.—Codosiga umbellata; a few colonies of Zooids diverging from the parent foot-stalk with flagella extended, magnified 650 diameters.
Ciliata.—Types of Ciliata obtained from hay infusions are very numerous. Ehrenberg’s animalcules were mainly of a large size, and of those belonging to the higher order of the Ciliata, pertaining to such genera as Paramecium, Colpoda, Cyclidium, Oxytricha, and Vorticella. These, however, represent but an insignificant minority of the hosts of flagellate forms which abound in our humid climate, and in hay infusions in particular. In such infusions, watched from day to day and produced from hay obtained from different localities, the number of types developed in regular sequence is found to be perfectly marvellous, commencing with the Monas proper, Amphimonas and Heteromita; while Bacteria, in their motile and quiescent forms, are invariably present and furnish an abundant supply of material for the microscope.[67]
Vorticellidæ constitute one of the most numerous families of the ciliate infusoria. All its members are at once recognised by their normal stationary condition, and by the structure of their oral system. In but few of the genera is there any marked divergence from this formula, and when any exists it is made manifest by an increase in development of some one of its elements at the expense of another. For instance, in the genus Spirochona, the external edge of the encircling border or peristome is suppressed, while the inner portion is abnormally developed into a transparent and highly elevated spiral membrane. The bell-animalcules usually possess stalks, and are either solitary or form branching colonies. Conichilus vorticella ([Plate III]., No. 80) is a well-known member of the colony stock, all the zooids of which are united on a slender branching pedicle, which consists of a central contractile cord enclosed within a tubular hyaline sheath. There are many other shrub-like colonies all variously modified in form and character. The Epistylis opercularia, or nodding-bell animalcule, is an interesting member of a numerous host of solitary short-stalked forms ([Fig. 337]). When the animal is disturbed, the heads drop down towards the stalk. This animalcule has been found to form a colony; and another, Carchesium, whose tiny branched tree-like colonies resemble little white globular masses of moulds, are seen at once to drop down towards the base of the colony with a jerky movement if the cell be touched. By a process of encysting, all the Vorticellæ and many of the more highly-organised ciliata have the means of what may be termed self-preservation. Should the water dry up in which they have been living, the little animal encases itself in mud at the bottom of the pool. Should this be baked by the sun not the least injury arises, for at this stage it crumbles into dust, and is carried by the wind to long distances, but the first shower of rain calls it back to active life, and soon after it is seen to issue forth as a free swimming bud.
Fig. 336.—Vorticella microstoma.