ANNULOIDA : KOTIFERA. 157 



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. 



The nervous system of the Rotifera constitutes a cerebral 

 mass, ' which for its proportionate volume may compare 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? 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 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 

 (Hi/datinea 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 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 

 muscles. These natatory organs are considered by Mr. 

 Gosse to be homologous with the articulated limbs of the 

 Arthropoda. 



In AsplancJma, whilst the masticatory organs, gullet, and 

 stomach are well developed, there is no intestine, the stomach 

 ' hanging like a globe in the centre of the body-cavity.' 



AFFINITIES OF ROTIFERA. In their external appearance, the 

 Rotifera approximate closely to the Infusoria, but the organisa- 

 tion of the former presents a very striking advance when com- 

 pared with that of the latter. Thus, in the Infusoria there is 

 no differentiated body- cavity, bounded by distinct walls, and 

 the alimentary canal is imperfect, the digestive sac simply 

 opening inferiorly into the diffluent sarcode of the centre of 

 the body. Further, there are no traces of a nervous system, 

 and the contractile vesicles, if looked upon as representing the 

 water- vascular system, are a very rudimentary form of this 

 apparatus. In the Rotifera, on the other hand, the alimentary 

 canal forms a complete tube, having an oral and an anal aper- 



