ANNULOSA: ROTIFERA. 



251 



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 

 Rotifera, and in summer the eggs 

 are produced by the females without 

 having access to the males. De- 

 velopment is direct. 



The muscular system of the Ro- 

 tifera is well developed, consisting 

 of bands which produce the various 

 movements of the body and foot, 

 whilst others act upon the various 

 viscera, and others effect the move- 

 ments of the jaws. 



The typical group of the Rotifera is that 

 of the Notommatina (Hydatinea of Ehren- 

 berg.) In this group (fig. 123) the animals 

 are all permanently free, and are never 

 combined into colonies, while the integu- 

 ment is flexible, and the body is never en- 

 cased 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. 122, B) inhabits a 

 tubular case, which the animal forms for 



itself by means of a special organ for the F ; g I23 . Rotifera. Eosphora au- 

 purpose ; whilst Polyarthra and Triarthra r ita, one of the Wheel-animal- 

 are protected by a stiff shell, or "lorica." cules. Enlarged about 250 dia- 



In Triarthra there are ensiform fins, meters " < After Gosse ' ) 

 jointed to the body by distinct shelly tu- 

 bercles, and moved by powerful muscles. These natatory organs are con- 

 sidered by Mr Gosse to be homologous with the articulated limbs of the 

 Arthropoda. Locomotive appendages are also present in Hexarthra, Polv- 

 arthra, and Pedalion. 



In Asplanchna, 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, " but not communicating with the body-cavity. 



As regards their distribution in space, the Rotifera have an 

 almost world-wide range. The majority of the known forms 

 are inhabitants of fresh water, but a few live in the sea. 



