VII PARTHENOGENESIS 263 



several hundreds of the Apus from the pond, he never 

 found a single male amongst them. On one occasion 

 he had the whole contents of the little pond removed 

 with the greatest care, so as to feel sure that he had 

 obtained every Apus present. He received on this 

 occasion 5796 specimens of Apus, every one of which 

 being carefully examined proved to be female. At 

 the same time 2576 specimens of Branchipus were 

 obtained from the pond, which were, as usual, of both 

 sexes. In those cases where ponds afforded both 

 males and females of Apus, it is remarkable that the 

 proportion of the sexes was very variable. The 

 highest proportion of males appears to be in a case 

 recorded by Sir John Lubbock, who found thirty-three 

 male and thirty-nine female Apus productus in a 

 pond near Eouen, whilst among 193 specimens of 

 Apus cancriformis, from a locality near Krakow, 

 only one male occurred. What is most important 

 about this variation in the proportion of males to 

 females is that in two or three localities, furnishing 

 mixed generations of Apus, from which he has received, 

 year after year, numbers of specimens, Siebold has 

 observed an apparent constantly-augmenting dispro- 

 portion of males to females, and he is led to the 

 supposition that in these cases the males will at last 

 cease altogether, and thus a female generation be pro- 

 duced which will continue to reproduce itself partheno- 

 genetically, as in the Gossberg and a great number of 

 other ponds. This is, however, by no means proved ; 

 and we have no idea at present as to how the males 

 may make their appearance again, or what are the 



