454 OLIGOCHAETA 



to the spermathecae. Again, the presence of two pairs of spermiducal glands, so 

 characteristic of Gordiodrilws, is not universal in that genus ; for G. ditheca, in other 

 respects extremely near to G. elegans, has but one pair of these structures ; and, as 

 I point out elsewhere (below), there are no reasons for regarding this species as having 

 been described from individuals that were, in this particular, immature. The median 

 unpaired calciferous gland of the typical Gordiodrilus is distinctly paired in G. robustus ; 

 nor is it permissible to found generic distinctions upon the paired or unpaired 

 condition of an organ which a more profound study of the Oligochaeta shows to 

 be an impossibility. The fact that in all the species of Gordiodrilus the sperm-ducts 

 open quite independently of the spermiducal glands would be a slender basis for 

 distinguishing two , genera ; and, moreover, we are relieved from all temptation to 

 lay stress upon this character by the existence of different species of Ocnerodrilus 

 in which the sperm-ducts are, and are not, separate up to their very opening from 

 the spermiducal glands. But, in spite of these undoubtedly close resemblances, 

 I prefer to keep the genera separate, on account of the different segment on which 

 the sperm-duct opens, and its distinctness from the spermiducal gland. 



There is a question whether G. tenuis is really congeneric with the other forms ; 

 unfortunately I was not able to give anything like a complete account of the 

 anatomy of this species (29). In the meantime its differences from the other worms 

 are not insignificant. In the fii'st place the transference of the male genital pores 

 so far back is a not unimportant character ; it is true that such a variation in the 

 position of these pores is found in species undoubtedly belonging to the same genus; 

 Buchholzia is an instance to the point ; but with the present worm there are other 

 differences ; the testes are but a single pajr, and the enlarged ventral setae are 

 another peculiarity ; so also is the great extent of the clitellum. 



The presence of calciferous glands in the ninth segment, and the structure of 

 the spermiducal glands is not absolutely distinctive of the genera Gordiodrilus, 

 Nannodrilus, and Ocnerodrilus ; the family Acanthodrilidae contains a genus, Kerria, 

 represented by two species, which shows a perfectly similar character ; the calciferous 

 glands are in the ninth segment, and the speripiducal glands are lined by a single layer 

 of epithelium. In possessing no penial setae this genus differs from the vast majority 

 of Acanthodrilidae ; but this is not unknown in the family, for in the genera 

 Benhamia, and Acanthodrilus, there are species without penial setae. In spite of 

 the resemblances between Ocnerodrilus and Kerria, I think that it is necessary, in 

 the present state of our knowledge, to place them in different families, though the 

 existence of these forms shows how difficult it is to distinguish the two families, 

 Cryptodiilidae and Acanthodrilidae ; at present the Acanthodrilidae differ from all 



