AN ATTEMPT TO CLASSIFY EARTHWORMS. 277 



This condition is retained in Moniligaster^ where, too, the 

 ducts are limited in length, passing through only one septum, 

 and have their external aperture more nearly in the position 

 common to the majority of water- worms than in any other 

 earthworm. The single pair of sperm-ducts (and testes) is 

 retained in the family Geoscolecidse, in which, too, we find 

 the sperm-sacs occupying, as in Tubifex, several somites. In 

 Typhseus, again, this primitive character is retained. The 

 size of the ovisac in Moniligaster recalls the fact that the 

 ova in water-worms after separation from the ovary push the 

 septa back, and come to occupy several somites. 



When a second pair of sperm-ducts appeared, each would 

 have its separate external aperture ; but (except in Perichseta 

 stuarti, A. G. B.) the two pairs of apertures have dis- 

 appeared; the two sperm-ducts become more or less fused 

 together; and as in the case of setse and nephridia this 

 fusion commences posteriorly and gradually ex- 

 tends forwards. Thus in Acanthodrilus, and in Eu- 

 drilus and Megascolides, the two ducts remain separate 

 till they join the prostate; in Microchseta they remain 

 separate through several somites ; finally, in Lumbricus and 

 others, the two unite immediately behind the second rosette. 



The Prostate. — In the majority of water-worms there is an 

 enlargement of the sperm-duct near its pore, and this enlarge- 

 ment may have glandular walls ; this condition is retained 

 in Moniligaster barwelli. In the rest of the earthworms, 

 when present, we have either (a) a diverticulum of the sperm- 

 duct, {b) a single pair of sacs opening independently of the 

 sperm-ducts, or (c) a couple of pairs of separate prostates. In 

 all the prostatiferous earthworms except in Acanthodrilidse 

 we find either (a) or (6). Dichogaster has prostates of both 

 varieties. No doubt the tubular prostates, as seen in these 

 latter and in other genera, are more primitive than the branched 

 prostates of Perichseta, the flattened condition seen in 

 Cryptodrilus and Perionyx leading towards this. 



Moniligaster barwelli is, in this matter, more primi- 



