The Determination of Sex 



371 



This means that in Diplogaster robustus there is i male to 

 10,000 females, and in Rhibiditis viguieri i male to 450 females. 



There is nothing in the structure or in the organization of 

 these superfluous males that would lead us to consider them im- 

 perfect. In every point of their organization they correspond 

 to the ordinary type of the males of unisexual species. Even 

 the testis is normal and produces spermatozoa which are identical 

 in form, size, and structure with those in the hermaphroditic 

 glands of the corresponding females. On the oth-er hand, these 

 males have nearly lost their sexual instincts, and are rarely seen 

 to pair with the hermaphroditic females. 



Maupas carried out the following experiments. He placed 

 males and females together for a number of days and recorded 

 the number of times fecundation took place. It will be observed 

 that more that half of the cases occurred in Rhabditis marionis, 

 in which it is known that the hermaphroditism is incomplete. 



Thus 313 females put with 272 males gave only 20 fecundated 

 females. In all cases except R. marionis the sexual indifference 

 of the males is almost absolute. This is the more surprising, 

 since in other species of Nematodes with separate sexes the 

 copulation is readily observed and lasts for some time. Here, 

 then, we have a case of a psychical "decadence," unaccom- 

 panied by structural degeneration. The sexual process is being 

 replaced by hermaphrodite fecundation. 



This elimination of the male type in the Nematodes is shown 



