ANNULOIDA I ROTIFERA. 



20 1 



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 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 movement 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 {Hy da- 

 tinea of Ehrenberg). In this group 

 (fig. 74) the animals are all perma- 

 nently 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. 53, 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 en- 

 siform 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 F ^ 4 oT,hew,STS le r t'- 



With the articulated limbS OI the larged about 250 diameters. (After 



Arthropoda. 



In Asplanchna, whilst the masticatory organs, gullet, and 

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



