B. THE ANATOMY OF SOME AQUATIC 0LIG0CH.1ÎTA FEOM 



THE PUNJAB. 



By J, Stephenson, Major, I. M.S. 



NAIDID^. 



Nais variabilis, Piguet, var. punjabensis, var. nov. (PI. xv, fig. i.) 



The form here described was found first in the tank at Shalimar near I^ahore, 

 and afterwards in other places. 



Externa characters. — The animals are of an indefinite light grey colour, and are 

 fairly transparent under the microscope. The average length of a single individual 

 is about 5-6 mm. ; they may be only 2-3 mm., or on the other hand a fully extended 

 specimen about to divide may reach 12-14 mm. They live for the most part crawling 

 freely in the mud or on aquatic vegetation ; but in the month of May, a considerable 

 number were found concealed, probably temporarily, in the tubes of insect larvae. 

 I could not differentiate these tube-inhabiting forms by any certain means from 

 others previously observed. Backward progression is quite easy to these animals, 

 and is not uncommon, at least while under examination. 



The prostomium is short, slightly extensible, rounded, and bears sensory hairs ; 

 the surface epithelium is thicker at its tip than elsewhere in the body. The mouth 

 is transverse, reaching from side to side. The eyes are placed laterally exactly at 

 the level of the mouth ; they are ovoid or somewhat irregular masses of black 

 pigment, with, in addition, a violet tinge ; additional smaller eyes {" Nebenaugen ") 

 may be present near the two principal ones (fig. 3). In several cases (in the 

 posterior half of an animal which was about to divide) the eyes were being formed 

 by the deposition of a brown pigment ; in one case the pigment appeared to have a 

 violet tinge from the beginning. The body- wall is pigmented irregularly over the 

 few most anterior segments, in one case as far back as the ninth ; the pigment is of 

 a light brown colour, and is contained in the deepest portion of the body- wall, 

 probably in the epithelium lining the body-cavity. Behind the head the general 

 shape of the body is uniformly cylindrical. The anus is posterior and very slightly 

 dorsal. 



The number of segments is frequently about 26 ; but it may apparently vary 

 between 18 and 32, as computed from the number of ventral setal bundles; these, 

 however, diminish gradually in size at the hinder end of the animal, and cease 

 altogether some little distance in front of the anus [v. fig. 4). 



Asexual multiplication. — There is never more than one constriction present ; that 

 is to say, the chains of three, four or five incomolete individuals formed by Molosoma 

 or Chcetogaster are not found. Figure 5 shows the site of an approaching division ; 



