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 larve 
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 insufh- 
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 
