20 Hewitt, Cytological Aspect of PattJienogenesis in Insects. 



cytologically up to the present time. I am also unable to 

 fit in the facts which we find in Aphis with this theory, 

 Miss Stevens too, appears to find it difficult. In referring 

 to Castle's theory, Bateson (5, p. 127) says ' While ad- 

 mitting the likelihood of this suggestion, we feel that for 

 the present it should be received with caution. In par- 

 ticular, we doubt the conclusion that both ova and 

 spermatozoa (after a reduction division) are always bearers 

 of either the male or the female character. It seems 

 more likely that special cases will present special pheno- 

 mena in this respect.' 



Doncaster (34) in attempting to explain the phenomena 

 which he observed in the maturation of the unfertilised 

 eggs of the saw-flies, combines Castle's hypothesis of the 

 separation of male and female bearing nuclei with that of 

 Le Dantec, who considers that maleness and femaleness 

 are similar to molecular forces which cause an attraction 

 between bodies bearing them, comparable to bodies 

 charged with opposite kinds of electricity. In this manner 

 he explains the fusion of the inner polar nuclei in the 

 arrhenotokous forms by supposing that the &^^ nucleus is 

 $ and the three polar nuclei ? , $ and ? respectively, 

 proceeding outwards, so that there will be an attraction 

 between the two inner nuclei. In the thelyotokous forms 

 the &^^ nucleus is $, and the polar nuclei c?, $ and 9 

 respectively, there will be no fusion then of the inner polar 

 nuclei. His idea is very ingenious, but requires further 

 testing, as he admits. 



Another recent theory of sex is that of Ziegler (106) 

 which is based on the two assumptions that sex is a 

 character which can be transmitted by inheritance and that 

 the hereditary characters reside in the chromosomes. 

 The fact that Ziegler states that he knows that ' diese 

 Erklarung der Entstehung des Geschlechts nicht fiir alle 



