CLASS POLYPS. 



153 



proteus (PL 1, fig. 50), the neck is very distinct, a long gullet passing from 

 the mouth to the stomach ; but it is scarcely if at all discernible in the 

 ROTATORY Infusories. 2. In the POLYGASTKIC Class the Trunk is less 

 readily distinguished than in the ROTATORY, where it begins behind the 

 base of the wheel organ, but its dorsal and abdominal surfaces are readily 

 distinguished by the apertures of the mouth and vent being on the latter. 

 The genera Enchelys, Coleps (PI. 1, figs. 49 and 53), are exceptions, as 

 their mouth and vent are in the very centre of their extremities, and the 

 absence of eyes affords no other guide. 3. The Tail is all that part of the 

 animal beyond the vent, and may be compared to the foot of Molluscs. In 

 the POLYGASTEIC Class it is most simple, as in Astasia hccmatodes and 

 Amphileptus fastida (PI. 1, figs. 16 and 59). In the Vorticellince (PI. 1, 

 fig. 44), a long process is sent out, on the tip of which is a sucker. Its 

 simplest form, in the ROTATORY Class, is a mere lengthening of the soft 

 body from the abdominal surface, with a sucking cup, patella, at its 

 extremity, by means of which it can fix itself, as in Glenophora trochus and 

 Pterodina patina (PI. 2, figs. 11 and 34); sometimes a long stiff shank 

 supports the sucking cup, as in Monura, Mmocerca, &c. ; but the greater 

 number of this class have the tail bifurcated, as in Icthydium podura, Chae- 

 tonatus maxitmis (PL 2, figs. 9 and 10), &c., and in the genera Furcularia 

 and Euclanis (PI. 2, figs. 20 and 25) these forked processes are of con- 

 siderable length. In Rotifer, Philodina (PI. 1, figs. 29 and 30), and some 

 others, the tail is capable of retraction within itself like the joints of a tele- 

 scope; and such are often armed with little horny points, sometimes in 

 pairs, as in Rotifera ; sometimes in triplets, as in Philodina. 



Motive Organs. The organs of ,motion in Infusory animals are either 

 simple or compound. 



The most remarkable of the Simple Motive Organs are the Changeable 

 Processes, processus variaUles, which belong entirely to the POLYGASTRIC 

 Class, and result from the power which those animals possess, of protruding 

 at pleasure parts of their body into variously-shaped lobes and long tubes, 

 at one or many points at the same time or alternately, and hence arise the 

 protean changes for which many Infusories were so celebrated, but of which 

 the cause was not known till discovered by Ehrenberg. According to his 

 observation, this change of form depends upon the animal relaxing the part 

 to be protruded, and then, by the contraction of the rest, thrusting the 

 stomach and its contents against the relaxed part, and projecting it in a 

 finger or foot-like form, just as the hernial sac is produced by the intestine 

 being protruded from the belly. In this way is it that all parts of the 

 Anuelxe (PI. 1, fig. 21) can be thrust out into processes. But in the 

 Arcellince the projections can only be formed on the fore part of the body 

 and by the propulsion of a transparent fluid, not, as in the former case, of 

 the alimentary canal. The BaciUarice have also this remarkable property. 

 This power of changing form, and thrusting out processes, is well adapted 

 for pushing the animal along, in much the same way as a boat is pushed by 

 a pole. In many Infusories, stiff, straight, and long bristles, setae, are 

 observed, implanted in the animal substance, and are capable of slow eleva- 

 tion and depression. The Hairlets, cilice, by which the turnings about of 

 the Infusories are effected, are distinguished from the bristles by their bulb- 



shaped base, which, moving slowly upon their seat by means of a pair of 

 muscles, produce extensive circular swinging of their point; this can be 

 well observed in the larger species of Stylonychia (PI. 2, fig. 4) and Kerona. 

 In the Polygastric Infusories they are often spread over the whole body, and 

 are arranged in distinct rows, generally longitudinal, but sometimes trans- 

 verse ; sometimes they exist only about the mouth, and, in the ROTATORY 

 Class, on no part except on the wheel organs. The whole body is only 

 covered with these cilia in the Naked Infusories, with one solitary exception, 

 the genus Coleps (PI. 1, fig. 53), the armour of which consists of numerous 

 little pieces, placed in rows, and the interspaces studded with cilia. 

 Booklets, uncini, are sometimes observed, either ranged upon the abdo- 

 minal surface, as in Stylonychia (PL 2, fig. 4) and Euplotes, and serving as 

 feet or claws, or occupying the place of an upper lip, as in Glaucoma Colurus, 

 and Scaridium. Thick, straight, and very moveable bristles, called styles, 

 styli, exist in both classes of Infusories, having a distinct articular connection 

 with the surface of the body ; they are very distinct in Oxytricha cicada 

 and Stylonychia pustulata (PL 2, figs 3 and 4), upon the hind part of the 

 body, and seem to be employed for feeling. 



Compound Motive Organs belong specially to the ROTATORY Class of 

 Infusory Animals, of which they constitute one of the most remarkable 

 characters. They are formed by the collection and arrangement of nume- 

 rous cilia, or hairlets, about the front of the body, which turning or moving 

 upon their base independently of each other, produce an appearance so 

 closely simulating that of a wheel turning upon its axle, as to have led the 

 microscopist Baker to describe them as actually so formed, and hence has 

 been applied to them the name of Wheel Organs. The wheel organs are 

 either Monotrockous, i. e. have a simple connected ring of cilia, or the ring is 

 divided or manifold, as in the Sorotrochous Infusories. In the Monotrochous 

 section, the circle or wheel is of the most simple kind, and is placed near 

 the mouth, which is not contained within but on one side of it, interrupting 

 the ring, so that, instead of being circular, it has the shape of a horseshoe 

 closely set with cilia, between the heels of which the mouth is placed. If 

 the periphery of the wheel be regular, as in Ptygura melicerta, Ichthydium 

 podura (PL 2, figs. 8 and 9), such Infusories are called Holotrichous ; but if 

 it be indented and produced here and there into lobes, as in Microcodon 

 claws, Tubicularia najas, and Floscularia ornata (PL 2, figs. 14, 15, and 16), 

 such are said to be Schizotrochous. Two subdivisions of the Sorotrochous 

 are also observed, the two-wheeled or Zygotrochous, in which the wheel 

 organs are implanted on a pair of processes like arms, capable of protrusion 

 and retraction, situated close to each other, and between the mouth and 

 proboscis, as in Rotifer macrurus and Philodina acideata (PL 2, figs. 29 and 

 30). Those which have more than two wheel organs are called Polytrochous, 

 such as Hydatina brachydactyla, Euchlanis luna (PL 2, figs. 19 and 25). 



The use of the cilia, whether simply disposed about the mouth or forming 

 wheel organs, is to produce a current in the water by means of which the 

 food is brought to the mouth, and also to serve the purposes of locomotion 

 by swimming, which in some genera, as in Philodina, is restricted to 

 crawling, like leeches, prior to the development of the wheel organs. 



CLASS XV. POLYPS. 



ALTHOUGH in the living film which overspreads the Sponges, no distinct animal form can be observed, yet in that which envelopes the 

 several kinds of marine productions, commonly known as Madrepores, Corals, &c., and which have either a cartilaginous, horny, 

 or calcareous substance, distinct animal forms are seen, of a jelly-like, semitransparent nature, cylindrical in form, with an intestinal 

 cavity having a mouth surrounded by many lengthy processes or arms (whence their name POLYPS), and their opposite extremity 

 or foot attached to the cavities in which they reside. The whole animal is capable of motion, by the expansion and contraction 

 either of parts or the whole of its entire mass, and thus can project itself to a certain extent out of its chamber, expand its arms or 

 tentacules, and sway both them and its cylindrical body in all directions so as to bring it in contact with the prey it desires to 

 seize, around which it throws its arms, and clasping them conveys it to its mouth. The cavities in which these Polyps live are 

 called Poli/paries, which are either sunk in a mass of fleshy substance overspreading the axis or solid stem , supporting and giving 



