enter the Proteus, but that nutritive absorption takes place by the outer surface in this animalcule.

An animalcule nearly allied to Amaba has lately been discovered and accurately described by Professor Bailey, in the "American Journal," vol. xv., under the name of Pamphagus mutabilis. It consists of a soft, transparent, extensible tunic or body, capable of assuming every variety of shape, those shown at G and I, in Fig. 57, being the most common; around the mouth are a few branched tentacula, or

A, B, C, three very common shapes of the Amaba, or Proteus. D, Chilodon cucullulus. E, Paramecium aurelia. F, Leucophrys patula. G, H, I, K four different aspects of Pamphagus mutabilis.

feelers, by means of which these animals pull themselves along very slowly. The most remarkable feature the Pamphagus possesses, is the utter want of discrimination it seems to have in the food it takes; for fibres of cotton, linen and wool, starch, crystals of quartz and Diatomacea without end are swallowed by it, these are retained for a short time, and are then ejected by the mouth, which is the only aperture for their reception and discharge.

These animals, like many Polygastrica, are multiplied by spontaneous fission, as shown at H; occasionally, however, such masses as those represented by K are seen; these result from a swelling or distortion of the tunic produced by the quantity of ingesta combined with that of the partial spontaneous fission, or budding, of the animal.

We have here one of the simplest forms of animal life, consisting, it may be safely said, of little else than a stomach and certain organs for seizing food, its external framework, or rudimentary integument, being soft, colourless, highly elastic and extensible, and coloured yellow by tincture of iodine. In such creatures there is abundant evidence of the food being taken into the interior of the body, which was found not to be so satisfactorily proved in the case of the Amæba.

In all rapidly decomposing animal and vegetable substances, certain kinds of animalcules very soon make their appearance; one of the first-the Spirillum -is very minute and spirally twisted, like a corkscrew,

it is readily recognized by its worm-like movements. Amongst these may occasionally be seen gliding rapidly across the field of view, by means of well developed cilia, certain large flat animalcules, belonging to the genera Chilodon, Paramecium and Leucophrys, all of which, as shown by D, E, F, exhibit, more or less plainly, the complex nature, or rather the great subdivision of the stomach, by which these creatures are distinguished and classified. The stomachs, of most Polygastric animalcules, can be readily demonstrated by adding a small quantity of carmine or indigo to the water in which the animalcules are found; the particles of colouring matter are swallowed, and the stomachs are then easily distinguished from any of the other viscera. Vorticella nebulifera, or Bell Polype (Fig. 58), is,

FIG. 58.

A group of Vorticella nebulifera, showing the expanded and contracted

state of the stem.

as its English name implies, bell-shaped, with a large oral opening surmounted by active vibratile cilia, which produce currents in the surrounding water sufficiently powerful to form a sort of vortex or whirlpool, and draw other animalcules into its mouth. The polype is seated on an extensile and contractile filament, by which it is attached to submerged substances, and the filament extends and straightens when the cilia around the mouths are in active motion, but if another animalcule swims against it, or if a sudden shock be communicated to the microscope, the filament immediately coils up spirally, like a bell-spring, withdrawing the entire body from danger, while the cilia are retracted within the mouth of the animal. After a few seconds the filament is again gradually elongated, the cilia are extended, and their movements recommence with great activity. The addition of carmine to the water containing these animalcules, also causes a number of previously invisible stomachs to appear, and the small particles of the colouring matter in the surrounding water exhibit more strongly the action of the cilia. In this species of Vorticella the filament is simple and single, but other species exist, as, for instance, Charchesium polypinum (Fig. 59), in which the bodies are supported on branched filaments, each branch supporting a terminal body. The stem is highly contractile in V. nebulifera, in this species it is much firmer, and appears to contain a central cavity.

Very little can be said of the structure of the skeleton of the Polygastrica; it is either membranous or horny,

seldom, if ever, siliceous or calcareous, and presenting little, if any, traces of structure; the animalcules them

FIG. 59.

Charchesium polypinum, or Arborescent vorticella.

selves forming the chief food of some insects and fishes. The wheel animalcules were formerly included in this class, but recent investigations having demonstrated in them a far greater complexity of organization than belongs to the Polygastrica, they have been removed to the Articulate sub-kingdom, under the designation of Rotifera.

From the Polygastrica we pass to a tribe of animals which, from their arborescent forms, have obtained the name of animal-plants, or Zoophytes. These, on