Sexual Dimorphism and Polymorphism 311 



specific potential elements. And these could become 

 activated in the next following organism only when the 

 general distribution of its nervous energy should find 

 itself in the same conditions as at the time when this 

 new sexual character was acquired : a thing which 

 requires above all that the organism be of the respective 

 sex. 



In harmony with this the ordinary facts of embryonic 

 development teach us that as soon as the sexual organs 

 of one of the sexes become indicated, the accessory 

 organs just forming of the other sex cease to develop 

 and remain rudimentary, while the organs proper to 

 the sex which is already declared, both the essential and 

 the secondary, develop completely. There is thus an 

 arrest of growth in some organs from the fact of the 

 development of the others, which makes one suspect that 

 the conditions of environment created by this develop- 

 ment of some organs hinder the further activation of 

 energies which cause the production of organs of the 

 other sex. 



Thus there always remains latent the possibility, that 

 the characters of the other sex may also appear in an 

 individual already developed in the opposite way, espe- 

 cially in advanced age, when with the cessation of their 

 respective functions all the sexual organs and characters 

 lose their vitality; a thing which often occurs in many 

 species and in man himself, and which occurred partic- 

 ularly in that famous old hen which Darwin has reported, 

 which after having ceased to lay eggs took on not only 

 the voice, but the plumage, the spurs, and the fighting 

 temperament of the cock. 



One can say the same of polymorphism. In fact this 

 also can very well be regarded as dependent on an inter- 



