NOTES ON THE FKEE-]JV1N(^ NEMATODES. 461 



Sexual Instincts of tlie Males. 



Maupas' conclusion that the residual males could not take 

 any part in the production of offspring is expressed in the 

 following words: "Mais si ces animaux examines dans leur 

 structure et leur moi-phologie, representent des males vrais 

 et completSj il n'en plus de meme loi-squ'on les etudie au point 

 de vue de ieurs facultes etde leur activite sexuelles . . . ces 

 males ont a pen pres totalement perdu tout instinct et 

 tout appetit sexuels. . . . Nous trouvous en presence d'une 

 decadence psychique non concomitante avec une regres- 

 sion morphologique." 



This conclusion is supported by the inert behaviour of the 

 males, the fact that they are never seen in copulation with 

 hermaphrodites, but principally by the results of a fairly full 

 series of experiments which Maupas made with males and 

 hermaphrodites which had exhausted their own stock of 

 spermatozoa. Tiiese conclusively showed that the males have 

 almost, but not quite, lost their sexual instinct. One species 

 alone stands as au exception. In Rhabditis niarionis at 

 various times cultures containing in the aggregate 28 heruia- 

 phrodites and 42 males were kept under observation. Since 

 all the spermatozoa of the hermaphrodites were exhausted, 

 any production of developing eggs was plainly due to the inter- 

 vention of the male, and thus a measure of the activity of this 

 sex was obtained. Fertile eggs were laid by 13 individuals 

 to the total number of 150-200, and all these produced 

 hermaphrodites. This species is one of those for which 

 Maupas described a partially developed hermaphroditism, 

 and the author himself regarded it as specially significant 

 that in such a form the male should be less degenerate. 



The most 'complete series of experiments was made with 

 Rhabditis elegans. Here, in twelve cultures, a total of 

 139 hermaphrodites with their own sperm exhausted and 

 males were associated. X)nly six of the hermaphrodites were 

 actually fertilised, a proportion which illustrates exceedingly 



