34 SEXUAL DIMORPHISM 



unisexual variation and heredity by a modification of Darwin's 

 " provisional hypothesis " of gemmules. According to this 

 hypothesis, gemmules of infinitesimal size were given off by 

 all the organs and tissues of the body, and were accumulated 

 in the reproductive cells. It was the property of these 

 gemmules to develop again the organs and tissues from which 

 they were derived in the parents. Brooks suggested that the 

 male gemmules were more prone to variation than the female, 

 and therefore when they developed in a male individual they 

 gave rise to variations. The male, therefore, had a special 

 tendency to variation, while the female kept up the general 

 constancy of the species ; thus he attempted to explain why 

 it is that often in allied species the females are much alike, 

 while the males are very different. 



St. George Mivart regards the beauty of males and their 

 other peculiarities as the direct expressions of an internal 

 force. 



This view of the unisexual characters as due to internal 

 constitutional causes has been elaborated by Messrs. Patrick 

 Geddes and Arthur Thomson. 1 They argue that, essentially 

 and constitutionally, males incline to activity, females to 

 passivity ; that the physiological processes in the female 

 tissues tend to the passive accumulation of nourishment 

 and to growth, while in the male they tend to the active 

 production of movement and energy. When there is a 

 difference the female is in many insects and lower animals 

 large and stationary, the male small, agile, and often short- 

 lived. The details of secondary characters are due to the 

 abundance of diverse excretory products produced by the 

 more intense physiological changes in the tissues of the male. 

 To quote the words of these authors : " So brilliancy of colour, 

 exuberance of hair and feathers, activity of scent glands, and 

 even the development of weapons, are not and cannot be 



1 Evolution of Sex, 1889. 



