326 Records of the Indian Museum. [Voi,. X, 



dilates again to become the intestine before it has quitted segment 

 ix. The anus is dorsal. 



A lateral commissural vessel was seen in segment vi; no others 

 were noted, but it would perhaps be rash to say they do not exist. 

 The blood is yellow. 



The first nep /iridium is in segment vii ; thenceforward they 

 occur regularly. Each nephridial tube dilates to form a small 

 chamber in the parietes just before it opens externally in front of 

 the ventral setal bundle. 



The cerebral ganglion is large, extending forwards nearly to 

 Ihe tip of the prostomium and back to the level of the first bundle 

 of ventral setae. It is bifid posteriorly (text-fig. 2). 



Reproductive organs were not present in any of the specimens 

 examined. Asexual division, however, was taking place; ^=13 

 in the specimens examined. The first five segments and pros- 

 tomium of the hinder animal are formed in the budding zone. 



This species differs from most of those of the genus in having 

 no eyes. It resembles in some respects two specimens insuffi- 

 ciently described by Walton (16) under the name of N. tenui- 



2. 



F"iG. 2. — Nais yaviensis ; cerebral ganglion. 



dentis. It is useless, as Walton does, to describe the " ventral 

 setae"; in at least most species of the genus Nais and also of some 

 allied genera these differ widely in the anterior and in the succeed- 

 ing parts of the body. The points of difference usually extend to 

 the length, thickness, curve of shaft, position of nodulus, and 

 relative and absolute proportions of the teeth ; and no description 

 can fit both sets. In the present state of our knowledge, and 

 with the multiplication of species differing from each other in 

 comparatively minute points, the setae furnish the chief characters 

 for their discrimination ; and it is unfortunately impossible to 

 make use of a description which does not specify whether the 

 anterior or posterior group of ventral setae is meant, or whether, 

 as may perhaps happen, these are similar in character throughout. 

 The two groups are not distinguished by Walton in any of the 

 four species which he describes; yet it is in the highest degree 

 improbable that in all four cases both anterior and posterior 

 setae should be capable 6f description in the same terms. ' 



' The figure of the ventral setae given by Walton is stated to be of those of 

 segment ii ; the position of the nodulus, however, resembles what is usuall)' found 

 in more posterior segments. 



