THE ANATOMY. SPERMIDUCAL GLANDS 111 



upon which presumably the sperm-ducts open (the eighteenth) ; the two glands of 

 each side are, however, not similar to each other ; one is of the tubular variety, the 

 other like that of other Perichaetidae, i. e. ' racemose.' I was unable in examining 

 this species to discover with which, if either, of the glands the sperm-duct was 

 connected. 



Developmentally it might appear that the glandular part of the spermiducal gland 

 is distinct from the duct ; I have occasionally observed in immature Perichaetidae 

 the duct alone present ; and there are several species (Perichaeta masaJcatae, &c.) 

 in which the glandular appendix never seems to put in an appearance. 



The Eudrilidae have a characteristic spermiducal gland. It is superficially like 

 that of the Acanthodrilidae but really dififers in a number of peculiarities, which 

 together form one of the principal reasons for regarding the Eudrilidae as so 

 distinct a family of Terricolae, and for removing it from the neighbourhood of the 

 Cryptodrilidae. The gland has the same sausage-like form as in the Acanthodrilidae, 

 but has almost always a nacreous glitter owing to its thick muscular coat. The 

 main differences which distinguish the organ of the Eudrilidae from that of all 

 Megascolicidae are : — 



(]) The usually thick muscular layer; 



(a) The opening of the sperm-ducts into the glandular part ; 



(3) The presence of a terminal muscular sac (bulbus). 



As a general rule the glands in the Eudrilidae are distinguishable, as they are 

 in Acanthodrilus, &c., into a thicker glandular portion and a thinner duct, which is 

 lined by a single layer of non-glandular cells. 



This is particularly well marked in the genus Eudrilus itself, where it has been 

 figured by Peeriee, and by myself (see woodcut, fig. 30). 



In Eudrilus the muscular duct is very slender indeed as compared with the 

 glandular tube from which it arises. 



In a few other cases, however, there is no such abrupt transition. In Nemerto- 

 drilus, for example, the gland gradually dwindles towards the extremity which 

 bears the external pore; at the same time there is an increase, though a slight one, 

 in the thickness of the muscular coat ; and the lining epithelium becomes one layer. 

 In Heliodrilus there is the same absence of any pronounced demarcation between 

 the two sections of the tube, and the glandular lining becomes gradually one cell 

 thick ; it retains, however, its glandular character, being formed of large oval cells 

 between which are narrow packing cells ; but these disappear just before the opening 

 into the terminal sac. 



