Secondary Sexual Characters 437 



the uterus in such a way that it responds to the presence of the 

 embryo and grows up around it. 



It has been shown in the vertebrates that the development 

 of the secondary sexual organs is intimately connected with the 

 presence of the testes. In the insects it appears that this con- 

 nection does not exist. Oudemanns has shown for Ocneria dispar 

 that when the testes are removed from the male caterpillar, the 

 secondary sexual characters of the male are unaffected. Kellogg 

 has confirmed this result for the silkworm moth. Oudemanns 

 also removed the ovaries from the female caterpillar and found 

 that the female moth showed the normal markings. 



Pictet points out that in a few cases there exist a male form 

 and a female form of caterpillar, although as a rule in most ani- 

 mals the secondary sexual differences do not appear until the 

 adult stage. Often the size of the caterpillar is the only external 

 difference that is noticeable between the sexes, the males being 

 smaller than the females. In the case of Orgya antiqua and 

 Orgya gonostigma, however, the female caterpillars are superbly 

 colored, and covered with spines of different shades ; the male 

 caterpillars are not only smaller, but simpler and without the 

 spines. In Ocneria dispar the larval sexual dimorphism is 

 marked, but only in the fully formed stage of the caterpillar. 

 Pictet found that when caterpillars of this species are fed on es- 

 parcette and dandelion, that furnish ample nutrition, the larvae 

 develop with great rapidity, and all acquire the characters of 

 the female caterpillar. With pimprenelle, which also gives an 

 abundant nourishment, but not so well as the preceding, the 

 caterpillars that showed the female type of marking were in 

 excess. On the other hand, when fed on walnut leaves, giving 

 insufficient nourishment, the caterpillars all assumed the char- 

 acters of the male. In the case of other plants that gave insuffi- 

 cient nourishment this effect could not be seen, because the food 

 introduced other effects that changed the aspect of the caterpillar. 



The caterpillars of Ocneria dispar normally transform into 

 chrysalids after the fifth moult. The males reach the stage first 

 and the females may still be in the fourth period when the males 



