152 



CLASS INFUSOKIA. 



sucking Acalephs are of two kinds: 1. Those in which a simple cylinder 

 or pedicle depends from the centre of the concavity- of the body, as in 

 Geryonia (fig. 5). 2. Those in which from four to eight processes or 

 clas]>ers dip down, either distinct or connected together, as in Rhizostama 

 (fig. 9). 



3. The Siphonapharous Order are remarkably distinguished by the absence 

 of any stomach or alimentary cavity, and are divided by Eschscholtz into 

 three families : 



1. The Diphydous Acalephs, so named from their seeming resemblance 

 to two animals connected together, which originates in their body being 

 composed of two somewhat conical pieces, the apex of the posterior being 

 received within the base of the anterior. These pieces Quoy and Gaimard 

 describe as having an independent life, and capable of living for some time 

 after their separation. The anterior segment of the animal is considered by 

 Eschscholtz to belong to the nutrient part, and the posterior segment he 

 thinks is the swimming organ. The sucking claspers, of which there are 

 about twenty, are rolled up when at rest into as many little balls, but when 

 outspread, form delicate threads three or four inches in length, as in Diphya 

 (fig. 10). 



2. The Physaphorous Acalephs are characterised by a bladder containing 

 air, situated upon their upper extremity, by means of which they are floated 

 like hydrometers : hence Cuvier has applied to them the name Hydrostatic 

 Acalephs. The most simple form is that of Rhizophysa (fig. 11), in which 

 the transparent egg-shaped air-vesicle has its middle surrounded by hollowed 



pieces of cartilage, and from its lower end floats loosely its long tubular 

 body, from the .sides of which project the simple clampers, which, as in the; 

 preceding family, serve the pur|K>se of suckers. In Physophora (fig. 12), 

 the tubular alimentary canal is short; at its upper end is the air-vesicle, 

 and below it two rows of hollow cartilaginous pieces, which are followed 

 by a collar of delicate flask-like bags, containing fluid concealing the origin 

 of the claspers, which surround the extremity of the bodv, and of which the 

 form and length are very variable and elegant. The Physalice (fig. 13) ditii-r 

 from the preceding, in having no cartilaginous organs ; their air-vesicle is 

 large and oblong, with thick semitranspaivnt walls ; its long axis is hori- 

 zontal ; at one end there is an aperture by which the air cat) escape, ami 

 upon its upper surface a beautiful crest extends nearly throughout its whole 

 length, whilst beneath are sent down numerous tentacules and sucking 

 organs. 



3. The Veklidous Acalephs have within their soft substance a cartilaginous 

 or calcareous plate or disc, either circular or consisting of two pieces, by 

 the union of which an oblong body, either flat, or elevated to form a crest, 

 is produced. In Veklla (fig. 14) the disc is cartilaginous, consisting of 

 two pieces and oval; upon its upper surface is attached obliquely another 

 cartilaginous plate enveloped in muscular substance. In Porjiita (fig. 15) 

 the disc is round, calcareous, and marked above with concentric circles 

 traversed by radiating stripes, but has not any crest. The sucking organs 

 are in all the genera placed on the under surface, and the central one, which 

 is largest, has been considered analogous to a stomach. 



CLASS XI V. I NFUSORIA. 



THIS Division of the Animal kingdom, formerly considered by microscopic observers as exhibiting the most simple forms of animal life, 

 has of late years been shown, by the observations of Bory de St. Vincent, and especially of Ehrenberg, in most instances to 

 consist of very complicated structures, and generally to be far advanced above many animals which much exceed them in size. 



They are divided by Elirenberg into two Classes, the PoLYGASTRlC Class, in which the alimentary canal is divided into numerous 

 cavities or stomachs, and the ROTATORY Class, furnished with a remarkable organ, which, in its motions appearing to resemble the 

 turning of a wheel, is called the wheel organ. The latter class is more advanced in the scale of development than the former, but 

 it is convenient to consider them together, especially as they present many points in common as regards their covering and motive 

 organs. 



ILLUSTRATIVE EXAMPLES. 

 PLATES 1 and 2. 



External Covering. In both Polygastric and Rotatory Classes some kinds 

 have no special covering, such are called by Ehrenberg, naked, nvda ; whilst 

 others, inclosed in a sort of armour, larica, he calls covered, laricata. Of 

 this covering or armour he describes five kinds : 



1. The Shell, testa testula, a firm skin, often furnished with little teeth, 

 horns, spines, points, or warts. Usually hi the Loricated Rotatory Infusories 

 it is depressed, as in Brachinous amphuxros (PI. 2, fig. 33), but sometimes 

 compressed, and resembling a bivalve shell, for which it has been often 

 mistaken, as in Odiums caudatus (PI. 2, fig. 26). 2. The Target, scutellum, 

 scutelMum, seems to be peculiar to the Polygastric Class : it is firm, round, 

 or oval, smooth edged and only covering the back of the animal, as in 

 Aspidisca denticidata (PI. 1, fig. 60) and Euplotes Charon (PI. 2, fig. 7). 

 3. The Pitcher, urcedus, is a membranous or firm covering, often cartila- 

 ginous, bell-shaped, cylindrical, or conical, closed at bottom, open and 

 expanded in front, within which the animal can either retract entirely, or 

 project itself from it : as in Difflugia, proteiformis, Vaginicda crystallina 

 (PI. 1, figs. 22 and 48), and Floscutaria ornata (PI. 2, fig. 16). Some- 

 times, as in Ophrydium versatile (PI. 1, fig. 46). 4. The Cloak, or Mantle, 

 lacerna, which exists only in the POLYGASTRIC Class, is a thick gelatinous 

 mass or skin, apparently the external layer of the animal itself, expanding 

 with age, and under the protection of which, the internal parts of the body 

 freely divide, according to certain normal proportions, and inclose other 

 individuals which become loose upon the surface of the parent. After a 

 time this membrane loses its individuality, becomes subservient to the wants 



and will of the internal brood, and performs to them the office of a ti Ali- 

 mentary covering, as in Volvox globator (PI. 1, fig. 12). 5. The Bivalve 

 Target, larica bivalvis, exists only hi the large family Bacillaria, is of a quad- 

 rangular prismatic form, of a siliceous nature, and when drv splits into two 

 or more species, as in Navicula phamicentron and Bacillaria ndgaris (PI. 1, 

 figs. 28 and 29). 



In most of the Infusories, a head, trunk, and tail are distinguishable. 

 1. In the Polygastric Class the Head is scarcely discernible, but in the 

 Rotatory it is readily distinguished, forms the anterior part of the body, and 

 supports the wheel organ, eyes, mouth, and masticating organs ; in it also 

 is the great nervous ganglion, which Ehrenberg presumes to be the cerebral. 

 The mouth is generally placed beneath, and not precisely at the anterior 

 extremity, which is formed by the projection of the forehead, distinguished 

 by the red eye-spots, and often also stretches like a proboscis beyond the 

 wheel organ, as in Rotifer macrurus and Philodina aculeata (PI. 2, figs. 29 

 and 30), or drops into the anterior upper edge of that organ, as in Furcidariu 

 gibba and Diglena graiulis (PI. 2, figs. 20 and 21 ). Sometimes, as in Bra- 

 chionus amphiceros (PI. 2, fig. 33), the forehead is divided into three lobes, 

 covered with little hairy styles. In Rotifer, the eyes stand far forwards on 

 the proboscis, but in Philodiiia, on the contrary, they are backwards aboxv 

 and behind the mouth. Sometimes the nape of the neck is indicated by a 

 narrowing, but more commonly by the base of the wheel organ or by die 

 ]x>sition of the eyes. The mouth is often provided with a pair of lips, 

 which may be seen in both the POLYGASTRIC and ROTATORY Classes, as in 

 C/tilomonas volvox, Eugkna viridis (PI. 1, figs. 5 and 17), and in Melicerta 

 ringens (PI. 2, fig. 17). In the POLYGASTRIC Class, as in Lachrymaria 



