264 Proceedings of the Royal Physical Society. 



data with regard to these structures, which seem also to 

 exist in Brachydrilus} 



I have already pointed out that in Allurus^ the structure 

 termed atrium by Eosa,^ and therefore in all probability the 

 similarly termed structure in Allolohophora is really hardly 

 comparable to the atrium in any Acanthodrilini. It consists 

 merely of a thickening of the body wall, or rather of the 

 epidermis only, at the point of opening of the vasa deferentia, 

 similar in structure to the clitellum. This modification may, 

 however, conceivably be a last trace of an atrium ; it remains 

 to be seen what is the structure of that of Geoscolex, 

 etc. 



All these reasons lead to the inference that the Geoscolecini 

 are connected with the Acanthodrilini, and, as it appears to 

 me, more nearly to the Cryptodrilidse than to any other 

 family. But the fact that most of the genera of Geoscolecini 

 are much specialised in various directions, renders it difficult 

 to say which are the more centralised forms. 'No genus, to 

 my mind, can claim to be nearer to the base of the series 

 than any other. As to their connection with the Lumbricini, 

 that appears to be as Bosa has suggested, through Criodrilus 

 and Hormog aster. '^ The clitellum of Glyyhidrilus in its position 

 and extent approaches that of the Lumbricidse. 



I conclude this part of my paper with a recapitulation of 

 the groups and families, and with a " Stammbaum," which 



^ Benham says of this worm (Note on a new Earthworm — Zool. Anz., 

 No. 271, 1888) : — " There is no ' prostate ' or glandular diverticulum of the 

 distal end of the sperm duet ; but on each side is a very large muscular 

 (? glandular also) ' atrium,' as in Criodrilus and Titanus: this occupies about 

 six somites (xv. to xx. ), and is doubtless due, in part at least, to the con- 

 tracted condition of the worm, causing the dorsal wall of the above-mentioned 

 fossa to project inwards." 



^ On the Anatomy oi Allurus tetrccedrus (Eisen) — Q. J. M. S., vol. xxviii., 

 p. 365. 



^ I lombrichi del Piemonte, Torino, 1884, p. 52. The species of 

 Allolohophora in which the presence of an atrium is sjiecially mentioned are 

 A. profuga, A. minima, A. suhrubicunda, A. chlorotica, A. mucosa, A. 

 turgida, A. alpina, A. foetida, in fact nearly all. It is also found in 

 Lumbricus mclibceus and L. hcrculcus. In later papers its presence is men- 1 

 tioned in other species. 



* Rosa, Sulla Struttura dello Hormogaster Rcdii — Mem. R, Ace. Torino, 

 ser. ii., t. xxxix. 



