NEW SPECIES OF OCNERODRILUS. 229 



As regards the characteristics used to define the species 

 a few words may suffice. The genus appears naturally 

 divisible in two distinct groups, one in which the lower 

 part of the sperm ducts (efferent ducts) is enlarged and 

 shuttle-like, and one in which the duct throughout is of 

 even width. The form and size of the spermatheca 

 varies some, but Avithin certain limits it appears constant. 

 They are of the greatest value as species characteristics, 

 especially so the presence or absence of rudimentary di- 

 verticula. The lower part of the prostate appears very 

 constant as regards form and relative size. In some 

 species the muscular differentiation has progressed con- 

 siderably, in others it has hardly begun. It is inter- 

 esting to note that the three species which belong to the 

 latter class, also show other common characteristics, 

 which bind them together in one group. The relative 

 size and lobation of the septal glands, especially the one 

 in somite v, is of the greatest importance in determining 

 the species, and may be used to the best advantage. 

 The relative size and form of the sperm-sacs, espec- 

 ially those in somite ix and xii, are constant within cer- 

 tain Hmits, and are species characteristics of no mean 

 value. The relative thickness of the anterior septa is 

 also constant and should be noted. As regards testes, 

 ovary and oviducts, I have not been able to note any 

 great or constant differences. They appear all very much 

 alike, and are all constant in their location. The pres- 

 ence or absence of the setse in the inner couple of somite 

 xvii may also be used in determining the species. In 

 some species both setas are absent, in others only one is 

 wanting, and there appears to be a constancy as regards 

 which one of the setai in the couple. In one species 

 both seta? are present. The clitellum varies to some 

 small extent. It is much shorter in some species than in 



