NOTES ON THE FREE-LIVJNG NEMATODES. 478 



been produced a prolonged failure of spermatozoa, lasting- 

 twenty hours, occurred in one of the glands, so that 16 

 unfertilised eggs were laid with egg-shell, and the uterus 

 beside blocked by disorganised egg material, while the other 

 produced 40 fertilised eggs. After this interval developing 

 eggs were counted to the number of 300. 



(c) September 7th-12th, 168 fertile eggs. 



(d) „ 9th-20th, 730 



(e) „ 7th-17th, 362 



(f) „ 7th-10th, 81 



Out of the six individuals two laid about 700 eggs each, 

 and though the figures obtained from the others show a high 

 variability, this is partly to be explained by the very marked 

 influence which even a slightly unfavourable change in the 

 conditions can exert on sperm production. In cultures Avhere 

 several individuals are crowded together, it is noticeable that 

 very few eggs are laid, and that the uterus of the worms 

 speedily becomes crammed with disorganised eggs, shoAvino- 

 that the sterility is caused by the failure of the male, not the 

 female gametes. 



In conclusion, it must be stated that the hermaphrodite 

 species are apparently as successful as the bisexual species in 

 the struggle for existence, for they are found in equal, or 

 sometimes in greater abundance in nature. Evidently, though 

 the means of dispersal of the species is limited by their 

 generally low fertility, an advantage which more than counter- 

 balances is secured by the self-fertilising capabilities of each 

 individual. 



(3) Partial Hermaphroditism. 



It is here proposed to examine the description of certain 

 species which are said to form a genuine link between the 

 bisexual and hermaphrodite species. The species which 

 Maupas deals with ai-e Hhabditis marionis, R. duthiersi, 

 and E.. viguieri. 



(1) R. marionis. — A single hermaphrodite kept under 

 observation Avas found to lay only 129 fertile eggs, while 



