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- 
