South- American 'I'liliilicichu. 209 



Its chief distinguishing chariictor is the dark pigmentation 

 ot" the dorsal surface nt the botly ; the pigment j)ruved on an 

 examination of sections to be chietly located in the j)eritoneum 

 lining the dorsal side ot" the coelom, theuce extending for a 

 little way into the muscular layers of the body-wall and in 

 the opposite direction along the septa. The internal cha- 

 racters, apart from diUercnces of small im[)ortance, are those of 

 the following species. 



3. Hesperodrilus albus, sp. n. 



This is a small and slender species of a white colour (when 

 preserved) ; its general appearance is quite that of a Tabifex. 

 In addition to the peculiar characters of the ventral seta? 

 whicii 1 referred to as characteristic of the genus, this species 

 shows another peculiarity in those organs whicli I believe to 

 be unique in the Tubificida\ The dorsal sette do not com- 

 mence upon the first setigerous segment, but upon the 

 second ; there is thus the commencement of what Prof. Lan- 

 kester has termed " cephalization," so highly characteristic 

 of many Naids. Vaillant, in his recently published account 

 of the Oligoclia3ta, has united the Tubificids and the Naids 

 into one family; this species is a further proof of the justice 

 of this course. Not only does Hesperodrilus show in this 

 particular some resemblance to the Naids, but it also shows 

 an approach to the Luinbriculida3. It will be remembered 

 that in Phreatothrix and in Stylodrilus Vejdovskii the first 

 ])air of nephridia extend through a considerable number of 

 segments, though the funnel and the external pore are, as is 

 the rule, upon consecutive segments ; in Hesperodrilus alhus 

 we find exactly the same state of affairs. Tlie first pair of 

 nephridia are in the sixth segment ; thence they extend back 

 as far as the tenth, but the external aperture is upon the 

 sixth. The proof of this was not entirely derived from a 

 careful putting together of a series of consecutive sections, 

 which might possibly lead to error; in one section the course 

 of the tube through three segments was quite plainly visible. 

 Another mark of distinction between the Tubificidse and the 

 Lumbriculidge is thus broken down. I am disposed to unite 

 Tubificidse, Naidomorpha, and Lumbriculidge into one large 

 family. 



The spermathecai of this species are extraordinarily long ; 

 the genus as a whole is characterized by the possession of 

 long spermathecse, but the present species and the next one 

 have unusually long sacs, which extend through five segments. 

 Each sac is dilated at the blind end into an oval sac, in which 



