452 V. A. 1^(JT'J'S. 



(2) P r o p o r t i o n s o f ^I a 1 e s in H e r m a p li r o d i t e Species. 



Anotliev reinai-kal)le feature of the males of liermaphrodite 

 species studied by Maupas is their extreme rarity. In only 

 one out of eleven species investigated was he unable to find a 

 male; but in others males were only discovered by organising 

 cultures of very considerable size, contaiuiugseveral thousand 

 mature worms. So while in the majority of species the males 

 were less than 0"1 per cent, of the whole number of adults, 

 the proportion of 4 per cent, to which they rise in Rhab Jitis 

 marionis affords quitea striking contrast. In Diplogaster 

 maupasi, one of the species obtained from the Morfolk 

 Broads, the ratio of male to female is very much more 

 notable than anything which Maupas records, and does 

 occasionally approach, though remotely, that equality of the 

 sexes which is characteristic of the majority of animal forms. 

 In one large culture the males reached 10 per cent, of the 

 whole {'M7 i , 38 c? c?),aud in batches of eggs laid by the 

 same individual up to 30 per cent. (16 eggf>, Hi ,'>o S ^ ^^ 

 ^go^j 23^, 6(5" c?). These instances are, of course, specially 

 favourable, and picked from amongst scores of cultures which 

 did not yield a single male. It is very unlikely that a species 

 will be discovered uniformly consisting of equal numbers of 

 males and hermaphrodites. Southern i supposed that in 

 Rhabditis brassicte he had discovered such a species, but 

 ill a culture with which he kindly supplied me 1 have been 

 only able to find males and females, but no hermaphrodites. 



To illustrate the manner of occurrence of the males, I give 

 here an analysis of cultures of Diplogaster maupasi 

 carried on over twenty-five generations, from August, 1909, 

 to January, 1910. The whole series of cultures coinnieuced 

 with a single individual. In every subsequent generation at 

 least one hermaphrodite was isolated just before maturity to 

 carry on the succession. Wheu such an individual had com- 

 menced to lay eggs it was removed every day to another 



' Rowland Southern, " On the Anatomy and Life-History of Rhab- 

 ditis brassica; n. sp.." • Jouru. Eoon. Biol.." vol iv. 1W9. pp. 90-95. 



