ON THE ANATOMY OF HISTKIOBDELLA HOMAEI. 307 



segmentation Ijeai' out the conclusion that in the male and 

 female this region is composed of two segments. Haswell, 

 in Stratiodrilus, states that *'in the fourth segment the 

 nephridia are probably represented in the female by the ovi- 

 ducts, in the male by the vasa deferentia." I have shown 

 in the male and female that two nephridia are present in the 

 generative region, altliongh holding slightly different positions 

 in the two sexes. It is therefore impossible that the ovi- 

 duct and vasa deferentia represent transformed nephridia, 

 unless we consider the generative region to be composed of 

 three segments, for which there is no evidence. 



In my paper on the nephridia of Dinophilus taeniatus 

 I have given some reasons for opposing the view brought 

 forward by Schimkewitsch (28) and Harmer (12), that the 

 oviducts and vasa deferentia in the male of this animal 

 represent modified nephridia. IIei*e there are four pairs of 

 close solenocyte-bearing nephridia in the male and five in the 

 female. They show the same primitive relationship with 

 the blastoccfilic cavity as do those of Histriobdella. 

 Harmer's suggestion is that in the male the fifth nephridium 

 has been modified into the vesiculae serainales and vasa 

 deferentia, while it remains unmodified in the female as the 

 fifth nephridium. In the male he holds that one of the 

 pairs of nephridia has lost its primitive relationship with the 

 blastocoelic cavity, and here becomes highly modified into 

 the large ciliated apparatus of the vesicula seminalis and 

 the vasa deferentia. The principal evidence relied on by 

 Harmer in making this comparison is the resemblance of the 

 funnel-like opening of the vasa deferentia into the cavity 

 of the testis, to the funnels with which he thought the 

 nephridia were furnished. I have shown that these do not 

 exist, and that the nephridia of D. tseniatus are definitely 

 closed. Therefore the funnels of the vasa deferentia 

 cannot be derived through modification from those of the 

 nephridia. 



In Histriobdella and Dinophilus, I believe the ovi- 

 ducts, funnels, and vasa deferentia represent structures 



