158 EVIDENCE OPPOSED TO 



causes the characters of the male to appear, so that 

 the dominance of the female is not a permanent 

 condition of the soma but is dependent on the 

 ovarian hormone. 



In the hermaphrodite individuals mentioned above 

 the difference of dominance is on two sides of the 

 body instead of two different individuals. It may 

 also be remarked here that while it is very difficult 

 to believe that spurs were not due in evolution to the 

 mechanical stimulation of striking with the legs in 

 combat, and while specially enlarged feathers are 

 erected in display, we cannot at present attribute the 

 varied and brilliant colour of male birds to the direct 

 influence of external stimuli. 



In Lepidoptera among insects the evidence con- 

 cerning castration tends to prove that hormones 

 from the gonads play no part at all in the develop- 

 ment of somatic sexual characters. Kellog, an 

 American zoologist, in 1905 ^ described experiments 

 in which he destroyed by means of a hot needle the 

 gonads in silkworm caterpillars (Bonibyx mori), and 

 found no difference in the sexual characters of the 

 moths reared from such caterpillars. Oudemans 

 had previously obtained the same result in the Gipsy 

 Moth, Limantria dispar, Meisenheimer ^ made more 

 extensive experiments on castration of caterpillars 

 in the last-mentioned species, in which the male is 

 dark in colour and has much-feathered antennae, 

 while the female is very pale and has antennae only 

 sHghtly feathered. In the moths developed from 

 the castrated larvae there was no alteration in the 



1 Journ. Exper. Zool. (Baltimore), vol. i., 1905. 



2 Experimentelle Studien zur Soma- und Geschlechtsdifferenzierung, 

 Jena, 1909. 



