286 



Records of the Indian Museum. [Vol. XXII, 



species. This disparity in numbers is not, however, of universal 

 occurrence in the Viviparidae for Dr. Annandale informs me that 

 in tlie lyoktak Lake adult females of Lecythoconcha Iccythis were 

 at least as numerous as adult males, whereas in the case of 

 Vivipara oxytropis females were distinctly less numerous than 

 males. 



As I have already mentioned, examination of 50 examples of 

 the 1920 brood in July, taken from the pond in the Indipn 

 Museum, showed that the proportion of cf to 2 was 24 : 26. A fur- 

 ther examination of 35 examples from the same source in August 

 gave a corresponding proportion of only 15 : 20, so that there had 

 alread}' been a considerable drop in the proportion of <f examples 

 present. I give below a table showing the proportion of the two 

 sexes in individuals of different sizes. 



Table i. — Showing the proportion of sexes in individuals of 

 different sizes from the pond in the Indian Museum. 



This shows clearly that in the larger examples the proportion 

 of cr- sex is high whereas the exactl}' opposite condition prevails 

 among the smaller examples. We have alread}- seen that indivi- 

 duals of II mm. in length are of an age of three months or less, 

 and these must therefore have been born about the beginning of 

 June, whereas those having the greater length of 18 mm. were 

 almost certainly born in April or earlier. It seems clear then, that 

 at the commencement of the breeding season there is a very 

 distinct tendency to produce & offspring, whereas later in the 

 season it is mostly 9 examples that are produced. I am inclined 

 to attribute this alteration in sex-production to the variation in 

 external conditions. I know of no data that would enable one to 

 form an estimate of the length of the period of gestation, during 

 which the developing embryo is retained within the uterus, and 

 it probabty varies at different periods of the 3'ear, but it seems 

 likely that offspring born in April are derived from ova that 

 became mature and were fertilized during the winter season, 

 whereas offspring born later in the year will be derived from eggs 

 that became mature during the warmer weather. If this be so, we 

 have here another example of the influence of adverse surround- 

 ings in the production of male offspring. 



Food. 



A study of the contents of the stomach of a number of 

 examples, as well as observations carried out on living specimens, 



