80 ZOOLOGY. 



with which the anterior end of the body is furnished. 

 The mouth leads into a pharynx, which is furnished with 

 a series of hammer-like pieces, believed by Gosse to be the 

 representatives of the mandibles and maxillse of the 

 Insecta. The food having been crushed by these hammer- 

 like jaws, passes through a gullet into a large stomach, 

 which is succeeded by an intestine, terminating in a 

 cavity called the cloaca. 



112. Circulation. Nothing corresponding to the heart 

 and circulatory organs of the Arthropoda has been discov- 

 ered in the Eotifera. There is, however, a well developed 

 water vascular system. It communicates with the ex- 

 terior by an opening leading into a cloaca, which also 

 receives the excretions from the intestine and generative 

 organs. This outlet communicates with two complex 

 tubes termed respiratory tubes, which pass along the 

 sides of the animal, and terminate near the head. No 

 true organs of respiration have been observed. 



113. The nervous system consists of a single mass, situ- 

 ated in the head of the animal. This mass is of such a large 

 comparative size, that Gosse asserts, it "can only be com- 

 pared to the brain of the Vertebrata." From this ganglion 

 a pair of nervous threads proceed backwards. Such a 

 nervous system is very different from the double gan- 

 glionated chain found in the Annulosa. 



A red eye of simple structure is situated upon the gan- 

 glion. 



114. Development. In all the Rotifera the sexes are 

 distinct. The description given above applies only to the 

 females. The males are much smaller, and are entirely 

 without digestive or masticatory organs. They, how- 

 ever, possess the water vascular system in common with 

 the females. They live but a short time, their sole busi- 

 ness being to secrete sperm. 



The females deposit ova of a large comparative size. 

 The young do not undergo metamorphosis. 



115. Turbellaria (Lat. turbo, I disturb). These animals 

 their name from the currents they produce in 



