1 82 MANUAL OF ZOOLOGY. 



through a well-developed perivisceral cavity, and terminat- 

 ing posteriorly in a dilatation, or "cloata," which forms the 

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

 systems. 



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

 tem, 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 ter- 

 minate 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, wheK 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 Inseda, to which class he believes ^& 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 

 cerebral mass, " which for its proportionate volume may com- 

 pare with the brain of the highest vertebrates." It is placed 

 anteriorly, and usually on the dorsal aspect of the body, and 

 the eye — in the. shape of a red pigment spot or spots — 

 is invariably situated like a wart upon it. Other sense- 

 organs, probably tactile, are often present in the form of 

 two knobs surmounted by tufts or bristles, placed at the back 

 of the head. The ovaries constitute conspicuous organs in 

 the female Rotifera, but in summer the young Rotifers appeal 



