ON THE SEXUAL PHASE IN INDIAN NAlDIDyE. 457 



2S. On tlie Sexiiul Phase in certain Indian Naidid?e (Oligo- 

 cli<«ta). By Haru JIam Mehka, M.Sc, Professor of 

 Zoology, Hindu University, Benares*. 



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



(Text-figures 1-3.) 



I have recently collected in the neighbourhood of Agra a lai'ge 

 number of examples of the following species of Naididse and 

 Tubificidse, many of wliich are fairly comuion there : — 



Neds pectinata var. incequalis Stephenson. 



Nais communis Piguet, var. punjabensis Stephenson. 



Hcemoncds laurentii Stephenson. 



Ghcetogaster orienialis Stephenson. 



Choitogaster pimjahensls Stephenson, 



Dero limosa Leidy. 



Pristina longiseta Ehrbg. 



Branchiodrilas Jiortensis Stephenson. 



Branchiura soioerbyl Beddard. 



As is well known, the ISTaididie usually reproduce jisexually 

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

 been described. As Stephenson 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 genera, and the scheme of classifi- 

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

 set of characters, the form and distribution of the setfe.*' I 

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

 above species, Nais pectinata vav. imvqtuilis and BrancModrilas 

 Jiortensis ; 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 Naididas which have been observed by 

 Stephenson to become sexual in Lahore, considerably further 

 north than Agra, do so from February to May ; the rains are 

 there later and scarrtier than further south, and May, June, and 

 sometimes Jul}^ before the rains appear, when 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 winter. In Agi-a I found the sexual specimens 

 described below in the autumn — in this part of the coinitry the 

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

 the ponds begin to dry up in (3cto])er, and the cold weather 



* Couiuiunicated liy J. Stk^hrnso.v, D.Sc, F.Z.S. 



Phoc. Zool. Soc.--iy20, No. XXXI. 31 



