458 I'ROK. TIARU RAM MEHRA ON THE 



appears, as in Europe, to be the unfavourable season. Whether 

 the sexual phase makes its appeai-ance in spring or autumn, there- 

 fore, it seems to be a measure of protection against approaching 

 adverse conditions ; the ova, quiescent or developing slowl}'- 

 within the cocoon, are probably able to withstand such conditions 

 better than the adult animal. 



In the case of JShi Is jyecUnata why. i/icequalis, niter the attain- 

 ment of the full sexual phase, the alimentary canal in several of 

 my specimens was seen to degenerate ; the same phenomenon 

 has been noticed by Stephenson (3, 4) in Dero limosa and 

 Ilcemouais laureniii. 



Many specimens of Branchiura soiverbyi, Dero Iwiosa, BrancJdo- 

 dribts hortensis, and Hmmonais laureniii were found living 

 together in the mud of a pond near Sikandra, A similar curious 

 association of Branchiura sowerbyi and a species of Branchio- 

 drilus has been noted by Beddard (1) in the Victoria regia tank 

 in the Royal Botanic Society's Gardens in Regent's Park ; and 

 Branchiura sowerbi/i, Branchiodrilus hortensis, and a species of 

 Dero have been found associated by Stephenson under natural 

 conditions at Lahore (2). These three ai'e among the few genera 

 of Oligocha^ta which possess gills ; in Ha'inonais laurentii, the 

 fourth worm which I found in tlie association, though there are 

 no gills, the vascular system is, for one of the Naidid^e, particu- 

 larly highly developed. 



Nais pectinata var. in^qualis Stephenson. 



Since Stephenson had only spirit specimens at his command, 

 I prefix a short account of some features of the general anatomy 

 of this worm. 



My specimens Avere larger than Stephenson's, their usual 

 length being 8-10 mm., but when the worms are fully extended 

 it may reach 15-18 mm. The colour is light reddish brown. 

 The prostomium is bluntly conical. The worms exhibit active 

 wriggling movements. The number of segments varies consider- 

 ably—from 40 to 95. 



The ventral seta3 are 4-6 in a bundle, usually 5 ; the length of 

 those in the anterior segments (ii.-v.) is 97-105 /x,, of the rest 

 88-93 fji. The dorsal hairs were 306-332 /x, and the dorsal 

 needles 106-112 /x ; there is a slight indication of a nodulus on 

 the latter. 



The penial setie (text-fig. 1 ) are the modified ventral seta? of 

 the sixth segment. They are 4-6 in a bundle, 98-105 /x in 

 length, and are somewhat swollen near the tip, which is usually 

 not forked although it is slightly hooked. Only two setaj were 

 noted as being bifid at their free end, and in these the prongs 

 were short, blunt, and of equal length. The whole bundle has 

 somewhat the appearance of a fan, and arises to the inner side of 

 the male genital aperture, 



(3rdinarily the doi'sal seta^ begin in the sixth segnu'ut, as 



1 



