462 PROF. HAKU RAM MEHRA ON THE 



only in specimens which have reached full sexual maturity, and 

 considering the large size of the ova seem to be too minute to be 

 of any functional importance. 



The spermathecte occupy segment v., and their openiugs lie at 

 the anterior edge of the clitellum immediately behind septum 4/5. 

 The ampulla attains a maximum height of 105 yu; its posterior 

 surface lies near the mouth of the sperm-sac, while in front it 

 may push forwards septum 4/5 so as to encroach on segment iv. 

 The ampullfe when distended are ovoid, and meet and pi^ess on 

 each other in the middle line above the alimentary tube. The 

 epithelium is low and flat, except near the duct where the cells 

 are fairly high and cubical. There is a thin layer of circular 

 muscular fibres, and a few peritoneal cells on the outside. The 

 spermathecal duct arises anteriorly instead of from the middle 

 of the base of the ampulla ; it is slightly oblique in position, 

 cylindrical, about 45 /a in length ; its lining consists of closely 

 packed columnar cells with nuclei peripheral, and a fairly thick 

 coat of circular muscular fibres surrounds this epithelium. 



The clitellum covers more than half of segment v., and all vi., 

 vii., and viii. ; to the naked eye it is opaque white. The cells 

 are four times as high as the ordinary surface epithelium, are 

 vacuolated, and when fully developed lose their distinctness of 

 outline. The clitellum is absent from the regions of the body- 

 wall between the spermathecal poi-es and the male apertures. 



The alimentary canal undergoes great degeneration in the 

 sexually mature worm. Though known in Dero limosa and 

 Hcemonais laurentii^ the phenomenon has not so far been observed 

 in the genus Nais. In advanced stages of maturity the mouth 

 becomes closed ; the buccal cavity and anterior part of the 

 pharynx lose their lumen and become reduced in size ; the pharyn- 

 geal cells lose their distinctness of outline, and those of the 

 ventral wall are reduced in size, low and cubical. Behind the 

 piiarynx the gut is continued as a narrow band without a lumen 

 as far as segment xii. ; the cells lose their regular epithelial 

 arrangement, and the solid cord is, seen in section, smaller than, 

 or sometimes about the same size as, the ventral nerve-cord : 

 there may be small spaces here and there, filled with fluid ; there 

 are large blood-vessels around it, in close contact with it. 

 Behind the sperm-sac there are small cavities in the solid cord of 

 disintegrating cells ; but after segment xvii. the intestine, though 

 still najTOwer than in the normal worm, retains its proper form, 

 and is iined with columnar cells surrounded by chloragogen 

 cells ; the lumen is either empty or contains some granular 

 matter. Although the gut is thus degenei'ating in the anterior 

 part of the body, the nephridia are normal, the blood-vessels are 

 larger than usual, and the same is the case with the cei'ebral 

 ganglion ; the specimens manifested the characteristic wriggling 

 movements, and were thus in no way pathological. 



When such specimens were kept under observation for three 

 days, their anterior portions, containing the genital orga;ns, 



