2OO MANUAL OF ZOOLOGY. 



tains a very complicated masticatory apparatus. * The parts 

 of this apparatus are horny, and are believed by Mr Gosse 

 to be homologous with the parts of the mouth in Insects. 

 In the females of almost all known species of Rotifera the 

 intestinal canal is a more or less simple tube, extending 

 through a well-developed perivisceral cavity, and terminat- 

 ing posteriorly in a dilatation, or " cloaca/' which forms the 

 common outlet for the digestive, generative, and water-vascular 

 systems. 



In both sexes there is a well-developed water-vascular 

 system, usually consisting of the following parts : In the 

 hinder part of the body, close to the cloaca, and opening into 

 it, is a sac or vesicle, which is termed the " contractile bladder," 

 and exhibits rhythmical contractions and dilatations. From 

 the contractile bladder proceed two tubes " the respiratory 

 tubes " which pass forwards along the sides of the body, and 

 terminate anteriorly in a manner not quite ascertained. Attached 

 to the sides of the respiratory tubes, in all the larger Rotifera, 

 is a series of ovate or pyriform vesicles, each of which is fur- 

 nished internally with a single central cilium, which is fixed to 

 the free end of the vesicle. It is asserted, however, that these 

 ciliated vesicles communicate internally with the perivisceral 

 cavity with its contained corpusculated fluid. The exact func- 

 tion of this water- vascular system is not known, but it is most 

 probably respiratory and excretory. Dr Leydig believes that 

 water enters the perivisceral cavity by endosmose, where it 

 mingles with the absorbed products of digestion, to form the 

 so-called "chylaqueous fluid;" and that the effete fluid is 

 excreted by the respiratory tubes, and ultimately discharged 

 into the cloaca by the contractile bladder. Taking this view 

 of the subject, Mr Gosse believes that " the respiratory tubes 

 represent the kidneys, and that the bladder is a true urinary 

 bladder ;" and consequently that "the respiratory and urinary 

 functions are in the closest relation with one another." This 

 observer, further, finds a decided analogy between the above 

 system in the Rotifera and the long and tortuous renal tubes 

 of the Insecta, to which class he believes the Rotifera to be 

 most nearly allied. No central organ of the circulation or 

 heart and no organs of respiration are present, but the perivis- 

 ceral cavity is filled with a corpusculated fluid. 



The nervous system of the Rotifera constitutes a bilobate 



* The lower jaws, or "incus," consist of a fixed portion, the "fulcrum," 

 to which are attached two movable blades the " rami." The upper jaws, 

 or " mallei," consist each of a handle, or " manubrium," to which is hinged 

 a toothed blade, or "uncus." 



