DESCRIPTIONS OF GENERA AND SPECIES 



521 



Fig. 46. 



The generative system of the Acanthodrilidae is very characteristic : the testes and 

 the ovaries occupy the usual segments; as a rule they are upon the front walls of 

 their segments as is nearly universal; but in A. annedens, as was pointed out by 

 myself some years ago, the gonads are affixed to the posterior wall of their segments 

 in close connexion with the ducts of the generative 

 products, actually in contact with the funnels ; 

 Octochaetus is peculiar in that the ovaries alone 

 have this abnonnal position, the other gonads being 

 normal in situation. A few species have only one 

 pair of testes ; this is the case with Kerria spegaz- 

 zinii, and with A. pictus. In A. annectens, A. 

 paludosus, and Biplocardia the sperm-ducts run 

 within the thickness of the body-wall ; probably 

 this is so with other species, though the above 

 mentioned species are the only ones in which 

 this very unusual course of the sperm-ducts has 

 been described. The two sperm-ducts of each 

 side of the body remain separate until their 

 opening on to the exterior; it used to be thought 

 that each of them opened in connexion with one 

 of the spermiducal glands ; but it is now certain 

 that in many species, and it is probable that in 

 all, the sperm-ducts open separately from those 

 glands on to the eighteenth segment. The spermi- 

 ducal glands are long tubes' which are in com- 

 munication with the orifices upon the seventeenth 

 and nineteenth segments already referred to. 

 They consist of a proximal glandular and a distal 

 muscular portion; the glandular part of the tube 

 has in all the genera of the Acanthodrilidae, 

 except Kerria, a lining of two layers of epithelial 

 cells; its structure in fact is like that of the 

 clitellum; in Kerria, as in Pygimaeodrilus, Ocnerodrilus, and Qordiodrilus, the 

 spermiducal gland is lined by only a single layer of cells ; opening in common with 

 the^ spermiducal glands is a sac of penial setae in very many — the majority — of 

 Acanthodrilidae ; in a few species there are two kinds of setae, plain and ornamental, 

 in a single bundle ; these are absent in the genus Kerria. 



3X 



-^ 



OCTOCHAETUS THOMASI. 



G. Gizzard. D.v, Dorsal vessel L.v. Lateral 

 Sp.s. SperiQ-saos. B. Hearts. Ca. 

 Caloiferoios glands. At. Spermiducal glands. 



