438 Experimental Zoology 
have transformed. At this time the females resemble the males, 
and the secondary sexual differences come afterward, while the 
females are getting still more food. This difference in the 
amount of food may be the indirect cause of the secondary 
sexual differences in these species. 
In the crustaceans, Giard has found that when Stenorhyn- 
chus is attacked by a parasitic copepod, Sacculina fraissei, the 
reproductive organs are almost completely destroyed. When this 
occurs in the male the female characters appear — the smaller 
claws and broader tail. In the female there is a reduction of the 
abdominal feet, a condition characteristic of the male. If these 
effects are directly due to the removal of the sexual organs, as 
experiment might show, and not due to the effects produced by 
the parasite, whose roots penetrate to all parts of the body, then 
they differ from the cases in the insects and are like those of the 
vertebrates. As yet it is not possible to decide which is the true 
view until castration has been artificially induced. 
We have now passed in review the principal facts connected 
with the occurrence and development of the secondary sexual 
characters. We have seen that in the vertebrates their develop- 
ment is connected with the presence of the testes, but that this 
is not true for the insects so far examined. ‘This difference may 
be interpreted to mean that in the vertebrates, the stimulus for 
the development of these characters in the male comes from the 
reproductive organs. The ability to develop these parts must, 
nevertheless, be supposed to be latent in the body cells. In the 
insects the body does not require the stimulus of the reproductive 
organs to develop the characters of the male. This distinction 
raises the question as to whether the secondary sexual characters 
of the vertebrates belong to the same class as the differences 
observed in insects, and this suggests the further question whether 
if they are different they may not owe their origin to different 
factors of evolution. 
LITERATURE, CHAPTER XXVIII 
(See Chapter XXIX.) 
