438 Experhnental 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 w^hen Stenorhyn- 

 chus is attacked by a parasitic copepod, Saccuhna 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 w^hich 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 abihty 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.) 



