276 W. B. BENHAM. 



remember that the separation of the couples and that penial 

 setae are present in various genera and families, I think it is 

 allowable to so regard it. 



The Position of the Clitellum. — In the fresh-water 

 worms (Microdrili) the clitellum is developed only during 

 the breeding season, and around the somite carrying the male 

 pore, or those immediately on each side of it. That is, the 

 " intra- clitellian " condition is the more primitive. 



Now, in Moniligaster sapphirinaoides the clitellum is 

 on Somites x — xiii, and the male pores between Somites x and 

 XI. The reason that it has not been observed in other species 

 of this genus is very likely due to the fact that it is present 

 only for a short period, during the actual breeding season. 



When the male pores shifted backwards, as they have done 

 in the rest of the earthworms, the clitellum probably accom- 

 panied them, giving rise to what Perrier called " lombriciens 

 intra-clitelliens : ^' in some cases the extent of the clitellum is 

 small, at other times it is great. But apparently in some 

 cases — Perichseta, Acanthodrilus, &c. — whilst retaining 

 its limited extent, it has not kept up its relative position, 

 coming to lie in front of the male apertures ; whilst in the 

 family Lumbricidse it is still further removed from its primi- 

 tive position, and lies far behind the spermiducal pores. 



The Sperm -ducts. — In the majority of the water-worms 

 (except Lumbriculidae) there is only one pair of sperm-ducts, 

 and this I regard as the primitive condition — that is to say, 

 when once the position of the genital glands had become fixed 

 to definite somites, and the nephridia specialised for the pur- 

 pose of conveying generative products to the exterior, there 

 was only one pair serving as sperm-ducts, and one pair as 

 oviducts ; previously to this state of things of course we should 

 get a less limited specialization ; but from general considera- 

 tions I believe one pair, and not two pairs (if so, why not 

 three pairs or four pairs?), of sperm-ducts was the typical 

 arrangement. 



