ON T]IE SKXUAL PJIASE I.V JXDIAX NAJDID.E. 



457 



28. On the Sexiuil Phase in certain Indian Nciidid^e (Oligo- 

 dwiUi). By Haku Ram Mehra, M.Sc, Frofe.-sor of 

 Zoology, Hindu University^ Benares'^. 



[Received June 15, 1920 : Read November 2, 1920.] 



(Text-figures 1-3.) 



I have recently collected in the iieighhourhood of Agra a large 

 number of examples of the following species of Naidida? and 

 Tubificidse, many of wliich ai'e fairly comuion there : — 



Nais pectinata var. iiicequalis Stephenson. 



jSfais coniviunis Piguet, var. punjabensis Stephenson. 



Hmmoiiais laurentii Stephenson. 



Clicetocjaster orientalis Stephenson. 



Chadogaster jmnjahensis Stephenson. 



Dero limosa Leidy. 



Pristina longiseia Ehrhg. 



Branchiodrilu.s hortensis Stephenson. 



Branch'mra sowerhyi Beddard. 



As is well known, the Naididjc usually reproiluce j'.sexually 

 by fission, and in many species the genital organs have never yet 

 been describetl. As Steplienson remarks (3), if such descriptions 

 " were available throughout the group, it can hardly be doubted 

 that we should be able to judge better of the affinities of genera, 

 and species, and consequently to improve our classification ; since 

 the diagnoses of species and <^enera, and the scheme of classifi- 

 cation, depend at present to an unduly large extent on one single 

 set of characters, the form and distrilnition of the seta^."' I 

 therefore give an account of the sexual organs in two of the 

 above species, Nais pectinaia var. inc^qimlis and Branchiodrilus 

 hortensis ; though the organs have been described in certain 

 other species of Nais, we have as yet no account of them in any 

 species of the genus Branchiodrilus. 



All the species of Naidida^ which have been observed by 

 Stephenson to become sexual in Laliore, considerably further 

 north than Agra,, do so from Februaiy to Ma\'; the rains are 

 there later and scantier tlian further south, and May, June, and 

 sometimes July, before the I'ains appear, wlien the ponds are dry 

 and the ground baked hard, represents the most unfavourable 

 season of the year for pond-life. In Europe these worms would 

 seem usually to enter on the sexual phase in the autumn, before 

 the rigours of Avinter. In Agra I found the sexual specimens 

 describe<l below in the autumn — in this part of the countrv the 

 rains are abundant from the latter part of June to September; 

 tlie ponds ])egin to dry uj) in Octol)ei', and the cold weather 



* (loinniui)ieated liy .1. SiKPirRisrsox, 1).Sc.. 1<\Z.S. 



Proc. Zool. SOC.--1920, No. XXXI. 3\ 



