162 OLIGOCHAETA 



however, it is not possible to base any such wide distinctions on the presence or absence of 

 'prostate' glands; since there are plenty of instances in which Intraclitellian male generative 

 pores are associated with the presence of prostate glands. 



The classificatory scheme of Vejdovsky (24) is in some respects an improvement of that of 

 Pekbiee. Benham carries in my opinion to too extreme a point the classification according to 

 the excretory system originally proposed by myself. 



It does not appear to me that any of the schemes advanced express the total facts 

 now known about the structure of the Oligochaeta. 



In the course of the following pages I have dealt with the mutual affinities of 

 the different families to one another ; and for all details the reader is referred to 

 these places. Summing up briefly the results put forward in detail, I may point out 

 that the Acanthodrilidae, Perichaetidae, and Cryptodrilidae, form a natural assemblage 

 which I make into a superfamily, Megascolides. In all the membei's of this group 

 (with very few exceptions) there are spermiducal glands which are unconnected with 

 the sperm-ducts, or into which the sperm-ducts only open near to their external 

 orifice ; these glands, too, are entirely without an external muscular sheath. Sharply 

 marked off by this character, the Megascolides are also the only Terricolae in which 

 there is a ' plectonephric ' excretory system, and they are the only group in which the 

 setae are often more than the ' typical ' eight. 



A group of equal importance is that of the Eudrilidae. In this group the 

 sperm-ducts open into the spermiducal gland always, and far up it in the glandular 

 part of the organ. This character does not, it is true, absolutely distinguish them 

 from the next family, that of the Geoscolicidae j but in the Eudrilidae there are so 

 many structures which are, without being universal, so widely spread and so peculiar 

 that it is, I think, necessary to regard the family as a distinct one. Such characters 

 are the presence of a system of coelomic sacs, involving the female organs of generation 

 and forming a spermathecal sac, the existence in the integument of organs probably 

 of a sensory function and of peculiar form ; the frequent network formed out of the 

 nephridial ducts and lying in the skin. 



The Geoscolicidae and the Lumbricidae are the only remaining families of the 

 Megadrili. 



Phylogenetic Aerangement of the Oligochaeta. 



The difficulty (greater in some cases than in others) of defining the various 

 families of the Oligochaeta seems to show that there can be no question here of 

 deriving the group from two or more stocks ; if we were limited to the types at 

 the extreme outskirts of the group such as Aeoloscmia and Endrilus, this view might 



