Although, at first sight, this might appear a very natural group, a little examination of their so-called rotatory organs will, suggest the propriety of separating frorn the rest the genera Floscularia and Stephanoceros. The organs which are called rotatory in those ge nera are evidently, as Dujardin has pointed out, more like to the bristles or setm of the lorica of other species, than to the true rota tory organs. The cilia, as they are called, of Flosczdaria, do not move at all. The bristle like organs of Stephanoceros are covered with cilia, which appear to be vibratile. The lo ricm of these animals also consist not of the integument rendered horny, but of a case secreted from the outside of the body of the animal. The animal has the power of retiring into this case, and in Stephanoceros this habit, combined with its structure, give to it a strong resemblance to some of the Cilio-brachiate Bryozoa. This external resemblance is so great, that many of the earlier observers re ferred it to the Polypifera. Oken referred it to the hydroid polyps, and placed it between Hydra and Tulndaria. Goldfuss referred it to a position in the same class between Coryna and Cristatella.
In the genus Lacinularia, the same ten dency to association exists, as is found in Conochilus.
The genera Floscularia and Stephanoceros constitute the first family of Dujardin. The remaining genera, previously noticed in this and the other families, are referred to his second family-.
Fanzily .5.—HYDATINMA. Charader. Na ked Rotifers, with a many-parted rotatory organ.
All the species of this family agree in the divided condition of their wheels, which do not consist of a circular or semi-circular row of cilia, but of several distinct rows or circles of such cilia, which are distinctly separated from each other. All the three forms, except Polyarthra, have an elongated pincer-like pro cess, proceedina from the abdomen, which resembles a tail:but is no proper continuation of the dorsal integument. In rnany species, a muscular apparatus is visible, by which the form of the body is changed. The nutritive organs in all cases are very obvious. It is niostly a simple conical intestine, which, in the great proportion of species, is without the constriction, which forms a kind of stomach ( fi'g. 293. d). Triarthra longisela (fig.297.) is, however, an exception, and exhibits a stomach formed by the constriction of the alimentary canal ; whilst Notommata myrnzeleo (fig.303. c) with some other species have a kind of gastric enlargement, terminated by a narrow anal ori fice. The commencement of the alimentary canal, with one or two exceptions, in all the genera, is supplied with jaws and teeth. Pancreatic glands are constantly present. The reproductive system is hermaphrodite. The ovarium (fig. 303. i) is elongated ; the eggs few. The male organs consist of two filiform elongated glands (fig. 303. g), and two contractile vesicles. The ova appear under two forms, one smooth and soft, the other hard and spinous. Kotonzmata brachionus, and the genera Polyarthra and Triarthra, bear their ova, like the Crustacea, attached to their sides. In several of the genera a vascular
system has been observed (fig. 293. ff, f,f), in the form of transverse and longitudinal vessels, the latter supplied with the tremulous organs called gills ( fig. 303.f, f). With this system, a kind of tap, or simple opening, in the neck (fig. 293. g) is connected. In fifteen of the genera, the two eyes, with their accompanying nervous ganglia (fig. 293. c), indicate the exist ence of a sensationary system. In Hydatina and other genera, nervous ganglia are seen in other parts of the body.
This family contains a larger number of species than any of the others. They are very generally diffused ; and Ehrenberg, in his microscopic labours, in many parts of the world, observed them in the north of Africa and the north of Asia ; they are commonly distributed throughout Europe. The loca lities they inhabit are very various, some are found in fresh water, other in salt. They are fond of confervm, and may be easily found nestling among these plants. They some times are in great numbers, so that they dis colour the waters in which they exist. The species of Triarthra give a milky opaque ness to the water in which they are found. The species of Polyarthra are interesting on account of the finlike organs which are de veloped at their sides, and by which they are able to move about. Several of the Notom mata are parasitic on other animals, and thus approach in habit some of the higher epizoa. The elongated setm or bristles of the species of Triarthra are also worthy of notice (fig. 297.).
Family 6. — EUCHLANIDOTA. CharaCier. Loricated Rotifers, with a many-parted ro tatory organ.
All the species of this family are clothed with a lorica, which resembles the exoskeleton of tortoises or crabs. Many of the species are remarkable for the appendages of the shield, as setce in Euchlanis and Stephanops, hooks (uncini) in Coluru:, horns (cornicula) in Dinocharis, spurs or respiratory tubes (calcar sipho) in Euchlanis (fig. 294.) and Salpina, a helmet (cucullus), in Stephanops. Most of the species have a furcated foot, some few of them have styliform feet. The interior of these animals is not so well observed as in families where the shield is of a less dense character. A muscular system, consisting of both longitudinal and transverse fibres, and muscles to move the foot, can be seen in most species. The nutritive organs consist of a muscular cesophageal head, furnished with two jaws bearing teeth. The cesophagus is mostly a short tube. In eight genera the alimentary canal assumes a conical form, in the re mainder it is constricted into a gastric organ. Two round or egg-shaped intestinal glands are present in all the species. The anal orifice is situated at the back of the basis of the foot (fig. 302. a). An ovarium with small ova, in four genera, Euchlanis, Monostyla, Stepha nops, and Squamella, are seen, in the form of tionary system is indicated •:by the presence of eyes, which are visible in ten genera and thirty three species.