208 Mr. F. E. Beddard on 



present species the branchiae, though apparenfly similar in 

 structure to those of Branchmra, liave a different arrange- 

 ment. In Branchiura they are dorsal and ventral, attached 

 to the median line of the body on those aspects. In Hespero- 

 drilus hranchiatus they are lateral in position, being attached 

 a little below the lateral setas. These were, moreover, in the 

 single specimen examined by me fewer in number; I counted 

 only thirteen ])airs. In the interior of each branchial process 

 was a capillary looj) ; their length is about the diameter of 

 the body ; no doubt during life they extend on each side for 

 a considerable distance beyond the body. It is an interesting 

 fact that in both the present species and in Branchiura the 

 branchiae should be limited to the tail-end of the body ; but 

 a consideration of the habits of the Tubiticidae seems to 

 explain this. It is well known that the common Tubifex of 

 our streams and rivers buries its head in the mud, while the 

 tail waves freely about in the water ; this appears also to be 

 the way with other Tubificids. Now in Limnodrilus the 

 hinder segments of the body are apt to have integumental 

 capillaries, which render the aeration of tiie blood easier in 

 those segments ; there is thus the first step in the formation 

 of a special breathing organ. In Bothrioneuron (see above) 

 the hinder end of the body is furnished with an exceedingly 

 rich integumental blood-plexus, which is a further step in 

 the same direction. Finally, we have in Branchiura Soicerhii 

 and in Hesperodrilus branchiafns the appearance of definite 

 branchial organs. On the other hand, in Choitohranchus 

 Sewperi, Bourne's gilled Naid, which presumably wanders 

 through the water and is not largely sessile, the branchite are 

 at the head end and diminish towards the tail; the same is 

 the case with Alma nilotica, whose nature, however, cannot 

 yet be regarded as certain ; it may be, as has b(?en suggested 

 by Fisig, a Capitellid. The branchire of Dero and of Aido- 

 phonis vuganSj if this genus be allowed as distinct from Dero, 

 are at the hinder end of the body. 



In other features of its organization this Hesperodrilus 

 conforms to the type of structure already described as charac- 

 teristic of the genus Hesperodrilus^ though there are naturally 

 other points of difference. 



2. Hesperodrilus niger, s[). n. 

 The most salient external character of this species is its 

 deep black coloration. It is a largish womi, quite an inch 

 in length, and of a considerable thickness. I regarded it at. 

 first as probably a Lnmhriculus. It proved, iiowever, in 

 dissection to be undoubtedlv a member of" this o;cnus. 



