168 



THE ANATOMY OF IXVERTEBRATED ANIMALS. 



sensory. Such are the ciliated pit and the spur-like process 

 (calcar) or processes, provided at the end with a tuft of setae, 

 which occur in many Rotifers, and are more or less closely 

 connected with the ganglion. In some there is a sac filled 

 with calcareous matter (otocyst?) attached to the ganglion. 



B 



Fig P&.—Hydatina senta (after Cohn).— A, female : a, anus ; &, contractile vesicle ; 

 c, water-vessels ; e, ovary ; /, ganglion. £, male : a, penis ; 5, contractile vesicle ; 

 c, testis ; /, ganglion ; g, setigerous pit. 



The ovarium and the testis are simple glands which open 

 into the cloaca, and are always placed in distinct individuals. 

 All the males at present known differ from the females in be- 

 ing much smaller, and in their digestive canal being arrested 

 in its development. The males copulate with the females, 

 and the eggs are sometimes attached to, and carried about by, 

 the latter — e.g., Brachionus. 



In some Rotifers, the eggs are distinguishable, as in cer- 

 tain Turbellaria, into summer and winter ova. The latter 

 are inclosed in a peculiar shell. In Lacinularia, it appeared 

 to me that the winter ova were segregated portions of the 

 ovarium, and that they were probably developed without im- 

 pregnation. Cohn, on the contrary, has given reasons for be- 



