274 Memoirs of the Indian Museum. [Voi.. I, 



is that this specimen has been separated by fission before the complete development 

 of the structures at the head end ; thus there are only three pairs of ventral seta ; 

 bundles in front of the beginning of the dorsal setse and these contain only one seta 

 each. Figure 52 shows an animal with eyes as yet on one side only. It seems possible 

 that this early separation may be the rule in the species ; but my observations do not 

 allow of a definite statement. 



The ventral setce are present in all segments from the second onwards. They 

 resemble those of the foregoing genera in type, being curved like an elongated / 

 the length varies from about -14 mm. (anteriorly) to -12 or -lo mm. (posteriorly); 

 they are forked distally, with the prongs of equal length, and the proximally situated 

 prong of the fork much stouter than the other. The nodulus is situated sHghtly 

 proximally to the middle of the length of the seta, and is a little more prominent 

 on one side than the other (fig. 36). There are usually three in a bundle, sometimes 

 two or four. 



The dorsal setce begin in the sixth segment. They are long and short, the long 

 being typical hair-setae, and the short probably having the same relation to these as 

 that surmised to exist between the long and short setae of Pristina {v. antea) ; that 

 is to say, they may be looked on as immature hair-setae, destined to take on further 

 growth when the long setae of the bundle drop out. In the sixth segment the long 

 setae may be as much as three times the body-diameter in length, about '8 mm.; 

 shorter lengths, for example one of two diameters, may be met with; these specially 

 elongated setae may be broken, or may exist only on one side.. In the remaining 

 segments their ordinary length is about the diameter of the body, or somewhat less 

 than this (max. 4 mm. ; more usually -3 — -25 mm.) ; they diminish somewhat in size 

 towards the hinder end of the body. 



These setae are frequently smooth ; but not uncommonly they present, like the 

 corresponding setae of iVajs and Pristina {v. antea), many fine thorn-like projections 

 (plate xviii, fig. 37), to which foreign particles may adhere. The explanation of these 

 " thorns" I take to be the one I have given for Nais variabilis ; and this is to some 

 extent supported by the fact that the setse in the anterior part of the body may be 

 found to possess these ''thorns," that is, to have become frayed out, while 

 the younger setae, at the hinder end of the body, remain quite smooth. 



The short setae are needle-Uke, -07 mm. in length, have no curve, end in a 

 single point, and may scarcely project at all from the surface of the body ; in any case 

 they are very short. Intermediate sizes between the long and short setae are not 

 found, or found only rarely. 



The general rule as to the composition of the dorsal setal bundles is that one long 

 and one short seta exist together in each. Two long setae are sometimes seen, two 

 short setae with one long one also occur; rarely a bundle occurs where no short 

 seta is visible at all. All setae may be absent from a bundle, perhaps in consequence 

 of injury. 



The body-cavity contains a large number of corpuscles. These are unlike those 

 of the previous genera ; they are very large, and the bulk of the substance of which 



