ANNULOIDA: ROTIFERA. 1/5 



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 peri- 

 visceral 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 of bristles, placed at the back of the head. 

 The ovaries constitute conspicuous organs in the female Roti- 

 fera, but in summer the young Rotifers appear to be produced 

 by the females without having access to the males. 



The muscular system of the Rotifera is well developed, con- 

 sisting of bands which produce the various movements of the 

 body and foot, whilst others act upon the various viscera, and 

 others effect the movements of the jaws. 



The typical group of the Rotifera is that of the Notommatina 

 (Hydatinea of Ehrenberg). In this group the animals are all 

 permanently free, and are never combined into colonies, while 

 the integument is flexible, and the body is never encased in a 

 tube. 



Stephanoceros and Floscularia, on the other hand, are fixed, 

 and are enclosed in a gelatinous tube which is secreted by the 

 animal. Melicerta (fig. 51, B) inhabits a tubular case, which 

 the animal forms for itself by means of a special organ for the 

 purpose ; whilst Polyarthra and Triarthra are protected by a 

 stiff shell, or "lorica." 



In Triarthra, there are twelve ensiform fins, jointed to the 

 body by distinct shelly tubercles, and moved by powerful 



