256 



Memoirs of the Indian Museum. 



[Vol.. I, 



the budding of new segments has taken place behind the sixteenth segment of 

 the original single animal, the first five segments of the posterior animal also have 

 been newly formed, so that the seventeenth segment of the original animal would 

 in this way become the sixth, or first with dorsal setae of the second. It may be 

 mentioned that I found [8 and 9] in Chcetogaster also that the first five segments 

 are intercalated at the head end of the second animal ; in Pristina, however {v. infra), 

 seven are so added ; and with these facts may be mentioned two others, that in 

 Chœtogaster and Nais the nephridia begin in the seventh, in Pristina in the ninth 

 segment; and that in Pristina the position of the reproductive organs also is two 

 segments further back than in the others. Figure 6 shows the hind end of an animal 

 which had apparently recently divided ; here the budding of new segments took 

 place behind the fourteenth original segment ; the site of the zone of budding would 

 seem, therefore, not to be a fixed one. 



The ventral setce (t^xt fig. i) occar in all segments from the second onwards; 

 but those of the second, third, fourth and fifth segments differ slightly from the 

 rest. All agree in being curved so as to resemble an elongated j , in being forked 



distally, the proximal prong being shorter and thicker 

 than the distal, in possessing a nodulus, and in project- 

 ing but slightly from the body- wall ; their total length 

 is at most about half the diameter of the extended 

 body. 



From the sixth segment onwards, they measure 

 •075 — -08 mm. in length, are moderately stout, and 

 have the distal prong of the fork j.\ times as long as the 

 proximal, though only f as thick at the base. The 

 nodnlus is distal to the middle, the proportions being — 



proximal to nodulus : distal to nodulus : : 4 : 3. 

 A variation in the relative form of the two prongs of 

 the fork was occasionally met with, where both were 

 of the same length, but the proximal prong was twice 

 as thick at its base as the distal. 



The ventral setae of the second to the fifth segments 

 are slightly longer, e.g., -09 — -095 mm. in a case where 

 the more posteriorly placed setae were 08 mm. They 

 are also considerably thinner ; the distal prong of the 

 fork is twice as long as the proximal, and is of the 

 same thickness at the base. Tiie nodulus is proximal 

 to the middle of the length of the seta, the proportions 

 previously given being about reversed, i.e. — 



proximal to nodulus : distal to nodulus : : 3 : 4. 



The usual number of ventral setae in a bundle is 3 to 5 ; numbers from 2 to 7 

 are also met with. 



Fig. I. — Ventral setee of Nais varia- 

 bilis, var. punjabensis — 



A, of ii, iii, iv, v segments; 



B, of the remaining segments. 



