626 OLIGOCHAETA 



The clitellum, incomplete ventrally, commences in front' of somite xviii, and occupies 



ten or more somites. 

 The spermiducal pores are behind somite xviii (with the exception of Hormogaster), 



and are usually nearly in the middle of the clitellum. 

 There are two or more pairs of sperm-sacs, and two pairs of testes and rosettes. 

 The spermathecae are either small, or, if large, are quite simple, without appendices. 

 The gizzard is in front of somite x. 

 Nephridia are provided with a large duct, usually produced into a caecum; nephridio- 



pores are in a line with the outer couple of setae (except in Hormogaster). 



To the first family belong the genera Geoscolex, Urochaeta, Diachaeta; to the second the genera 

 Khinodrilus, Microchaeta, Urohenus, Hormogaster, Brachydrilus. 



It will be noted in the first place, that Hormogaster, though referred to the second group, 

 dilfers in two important particulars from the remaining genera of its family ; these are duly 

 mentioned by Benham, but a third point of difference has escaped his attention ; this is the 

 arrangement of the setae. Hormogaster cannot be included in this family or in Benham's 

 Rhinodrilidae ; its isolated position must, I think, be allowed. 



With regard to the characters of the two families Geoscolicidae and Rhinodrilidae, the most 

 important distinction is the double nature of the male organs of generation in the Rhinodrilidae, 

 and the single pair of testes, sperm-ducts, &c. in the second family ; if we regard the presence of 

 one or two sets of gonads and ducts as being of little importance (as I think must be done in 

 view of such forms as Kerria spegazzinii), then there is not much left by which to distinguish the 

 two families ; the position of the gizzard in front of the tenth segment does not separate the 

 second from the first of Benham's two families, for in Pontoscolex (= Urochaeta) as he himself 

 correctly notes, the gizzard is in the seventh segment ; the characters of the spermathecae are no 

 more useful in differentiating the G-eosoolicidae from the Rhinodrilidae — as stated by Benham; 

 finally, the anterior nephridia — the first pair at any rate— of Ehinodrilus are larger than the 

 following ; this pair of nephridia are, as in Pontoscolex, modified into a ' peptonephridium.' 



At about the same time as this arrangement of the Geoscolicidae was published by Benham, 

 I (26) divided the group ' GeoscoKcini ' (= Rosa's family Geoscolicidae) into three families, viz.: — 



I. Urochaetidae. 



Setae irregular in distribution either throughout the whole body or after the first ten 

 segments or so. Prostomium absent. Spermathecae, three pairs. Calciferous glands, 

 three pairs. Nephridia with sphincter. A mucous gland present, being first nephridium. 



Genera — Urochaeta, Diachaeta, Onychochaeta. 



II. Geoscolicidae. 



Setae paired or distant (both conditions occurring in the same species). Prostomium 



present. Nephridia all alike. 

 Genera— Oeoscolex, Hormogaster, ? Glyphidrilus. 



•III. Rhinodrilidae. 



Setae paired or distant. Anterior set of nephridia different from posterior. 

 (jenera,— Microchaeta, Brachydrilus, Urdben^is, Ehinodrilus, ? Aniens. 



Though I believe that there is nothing in the above definitions contrary to fact, the classification 

 there suggested no longer commends itself to me; indeed, I pointed out at the time that these 

 families were not so satisfactory as those of the Aoanthodrilini. The two last families are the 



