1908.] J. Stephenson : The Anatomy of some Aquatic Oligochœta. 263 



as well as in a few other details ; and I cannot find in any one of them the exact 

 counterpart of. the form I have here described. Indeed it is perhaps hardly to be 

 expected that such a highly variable species should present exactly the same aspect 

 in such a distant region and different climate. 



There is, moreover, one peculiarity of the Indian form which distinguishes it 

 absolutely, so far as I have seen, from all forms of Nais hitherto described ; that is, the 

 frequent thorn-like processes on the dorsal hair-setse. Since these are by no means 

 always present, it would probably be better (accepting the explanation of the pheno- 

 mena previously suggested) to describe this as a general tendency or predisposition 

 to disintegration of these particular setae. 



That this characteristic has any greater value than that belonging to a geogra- 

 phical variety I do not for an instant suppose ; it occurs also in Pristina longiseta 

 and Slavina punjahensis (v. post.), and hence is in all probability connected with 

 local or climatic peculiarities. I would therefore suggest that the present form be 

 considered as a variety of N. variabilis, Piguet, to be denoted as var. punjahensis. 



Nais paraguayensis , Mchlsn. (PI. xvii, fig. 22.) 



This form was first found on April 27th in water from a pond in the Zoological 

 Gardens, Lahore. It is somewhat larger than the preceding, being from 8 to as 

 much as 20 mm. in length. It is of 'a light orange colour. It may progress at the 

 bottom of the vessel by active wriggling movements, or sometimes by undulations 

 freely through the water. There are no eyes. 



The prostomium is rounded, and not elongated. The anterior part of the body, 

 as far as the sixth segment, may be much thinner than the portion that succeeds 

 (fig. 22). There may be an immense number of segments ; on examining fig. 22, it will 

 be seen that the larger number, however, have probably been recently formed; rapid 

 budding seems to have taken place after the twenty-first original segment, twenty or 

 more new segments being indicated by the presence of small dorsal setae, and still more 

 by annulations and rudimentary septa, while at the extreme posterior end segments 

 are still altogether undifferentiated. In another case this budding took place after 

 the thirtieth segment ; rudimentary septa, but as yet no setae, were present in the 

 newly formed portion. 



The ventral setœ are of the previous type ; the prongs of the fork are of about 

 equal length, the proximal one being slightly stouter ; the nodulus is slightly more 

 prominent on one side than on the other (fig. 23). They are usually six in number 

 in each bundle 



The dorsal setce consist of both hair- and hook-setae. The hair-setae are equal 

 in length to the diameter of the animal, or sometimes somewhat shorter than this ; 

 they are smooth, and usually one, sometimes two, per bundle ; in the latter case the 

 second hair-seta may be considerably shorter than the first. The hook-setae (fig. 24) 

 are slightly curved distally in a sickle- shaped manner, and are very unequally 

 forked, the smaller prong of the fork being on the convex side of the ''sickle " and 

 much shorter and finer than the larger, which continues the axis of the curve ; these 



