ON THE ANATOMY OF HISTRIOBDELLA HOMAEI. 329 



nature of the limiting membr<ine, and fails to show the sharp 

 manner in which the testis is shut off from the general blasto- 

 coelic cavity surrounding the gut. He states that the testis 

 takes up the whole of the generative i-egion, which is not the 

 case, for the penis and its glands take up the posterior third as 

 I have mentioned. The anterior paired portion of the testis 

 is shown in section in fig, 39, while the niain unpaired portion 

 is shown in section in fig. 35. Internally the testis is filled with 

 a number of oval bodies, the spermatidia (figs. 27 and 35). 

 These consist of a number of nuclei with granular chromatin, 

 arranged round the circumference of a small mass of cyto- 

 plasm. In the region close to the anterior end of the testis 

 they form a solid mass, while in the middle they crowd its 

 cavity as a number of oval bodies. The mature spermatozoa 

 are found in the spaces of the testis cavity between them. 



If we regard the generative region as due to the fusion of 

 two segments, then this conclusion is supported by the arrange- 

 ment of the nephridia and the ganglia. The testis itself takes 

 up the first and largest of these, while the penis and accessory 

 glands take up the second. The division between the testis 

 and penis portion comes at just that point we should naturally 

 conclude that it should from the position of the ganglia. 



In the female the double nature of the generative region is 

 not so clear as in the male, and the metamerism is masked 

 by the extensive prolongation backwards of the ovarian sac. 

 In the young female, however, the ovary is confined to the 

 anterior two-thirds. The double nature of the generative 

 region then is almost as distinct in the female as in the male. 



The vesiculaj seminales are found in the posterior part 

 of the testis, and are pear-shaped bodies with their pointed 

 ends directed forwards. They are readily recognised on 

 account of the large quantities of sperm with which they are 

 always crowded. Leading into the lateral surface of each 

 vesicle is a fine duct from the granule gland. 



These are a mass of large mucus-like cells that lie against 

 the inner surface of the cuticle of the body- wall of the genera- 

 tive region. They secrete a granular mucous substance which 



