468 F. A. roTTS. 



from the appearance ot developing sperm-cells and egg-celU 

 in successive belts, for here cells lying side by side may give 

 rise respectively to spermatozoa and eggs. In one case tlie 

 sperm-cells seem to have been actually formed at the expense 

 of the ovum. The early maturation of the spermatozoa will be 

 noticed here, which terminates while young egg-cells forming 

 from a mother-cell of the same age have only completed the 

 first stages of their growth, 



(2) The Fertility of the Soi 1-ne matodes. 



The hermaphrodite species of Khabditis and Diplo- 

 gaster are distinguished from the bi-sexual, as Maupas points 

 out, by their lesser fertility, a character which indicates the in- 

 completeness of the hermaphroditism. In eleven of the twelve 

 species investigated by Maupas the number of fertile eggs 

 laid by a single hermaphrodite individual varied between 200 

 and 250, while in the twelfth (Rhabditis guignardi) the 

 limit of production rose to 500 or 520. Maupas states that 

 the female of a bi-sexual species is, on the other hand, capable 

 of laying 701) to 800 fertile eggs. The low fertility of the 

 hermaphrodites is due to the insufficieucy of the supply of 

 spermatozoa, for if to the number of fertilised egg^i be added 

 that of the unfertilised eggs laid when the male gametes are 

 exhausted, it may be seen that a hermaphrodite produces as 

 many eggs as the female in a bi-sexual species. Individuals 

 producing 200-250 fertilised eggs will afterwards lay two or 

 three times as many unfertilised,^ so that the total equals the 

 figure given for the bi-sexual species. 



Fertility, then, in these hermaphrodites is entirely controlled 

 by sperm-production, and probably the actual number of 

 spermatozoa formed in an individual is given or very closely 

 indicated by counting the eggs laid which develop into larva?. 

 In these experiments the eggs laid by each parent were 

 counted every twenty-four hours from the beginning o: 

 maturity onwards, and the mother then removed to a fresh 

 drop of peptone. Usually after about six days of active ovi- 



' Maupas. loc. cit., p. 587. 



