ON SOMATIC SEX-CHARACTERS 73 



ment of the rutting season, and development of 

 the antlers takes place between the beginning of the 

 year and the month of August or September. In 

 ducks and other birds there is a brilliant male-breed- 

 ing plumage in the breeding season which disappears 

 when breeding is over, so that the male becomes 

 very similar to the female. In the North American 

 fresh-water crayfishes of the genus Cambarus there 

 are two forms of males, one of which has testes in 

 functional activity, while in the other these organs 

 are small and quiescent : the one form changes into 

 the other when the testes pass from the one condition 

 to the other. 



It has long been known that the development of 

 male sex-characters is profoundly affected by the 

 operation of castration. The removal of the testes 

 is most easily carried out in Mammals, in conse- 

 quence of the external position of the organs in 

 these animals, and the operation has been practised 

 on domesticated animals as well as on man himself 

 from very ancient times. The effect is the more or 

 less complete suppression of the male insignia, in 

 man, for example, the beard fails to develop, the 

 voice does not undergo the usual change to lower 

 pitch which takes place at puberty, and the eunuch 

 therefore has much resemblance to the boy or 

 woman. Many careful experimental researches have 

 been made on the subject in recent years. The 

 consideration of the subject involves two questions : 

 (1) What are the exact effects of the removal of the 

 gonads in male and female? (2) By what means are 

 these effects brought about, what is the physiological 

 explanation of the influence of the gonads on the 

 soma ? 



