118 OLIGOCHAETA 



the 'atrium' of Tuhifex the peritoneum is absent from the ' Cementdriise,' which has 

 been shown by Vejdovsky to be an outgrowth of the lining membrane. I would 

 therefore compare the 'Cementdriise' of Tuhifex to a portion of the glandular 

 investment of the atrium in such forms as the Lumbriculidae ^ ; this view of the 

 relations of the different parts brings matters into a far more satisfactory condition; 

 and it helps us also to get a clearer insight into the meaning of the apparently 

 great difference between the spermiducal gland of the Perichaetidae and the Acan- 

 thodrilidae — in fact to compare more readily the ' lobate ' with the ' tubular ' form ; 

 in the class of gland which I have termed 'lobate' the lumen is much branched, 

 and the outer layer of glandular pear-shaped cells, instead of forming as it does in 

 the Acanthodrilidae, and in other genera which have the tubular form, a continuous 

 covering is broken up into masses of cells; now we get something very much like 

 this in the genus Telmatodrilus among the Tubificidae, and in Sutroa among the 

 Lumbriculidae ; but in neither of these genera is there any corresponding branching 

 of the lumen of the gland itself. Those Perichaetidae in which the gland is the 

 most compact, in which the branching is not so conspicuous, show the earlier stages 

 in the conversion of a tubular into a lobate gland — for example, Megascolex 

 newcotnhei, while Diplocardia is an almost ideal intermediate form ; there is in 

 fact no difEculty in getting the one form of spermiducal gland out of the other. 



I have now to consider certain points in the histology of the glands which 

 might seem to militate against a comparison between those of the aquatic and the 

 terrestrial genera. In the former the cavity is lined by a single layer of cells often 

 ciliated, which are separated by a layer of muscles from the outer layer of cells 

 which have been spoken of by some as ' prostates.' In the terrestrial Oligochaeta, 

 on the other hand, with a tubular spermiducal gland, the lining membrane is 

 with a few exceptions always composed of two distinct layers ; its resemblance 

 in fact to the clitellum has been often insisted upon ; I was inclined at one time to 

 contrast these two forms^ and to connect the resemblance of the spermiducal gland 

 of the higher Oligochaeta with the clitellum with its origin from the clitellar region 

 of the body : I do not now think that the difference is a real one ; in such 

 genera as Moniligaster it seems to me merely that the inner epithelial layer has 

 been removed a little way from the other layer, so that a layer of muscle has come 

 to intervene ; just as certain glandular cells, undoubtedly of epidermic origin, have 

 come to be imbedded in the musculature of the body-wall; the two cases seem to 

 me to be perfectly parallel. This view of the matter has been put forward by EosA 



' These views with regard lo tlie homologies of differently named structures are now those of Beniiam 

 (25) as well as of myself (80). 



