146 THE BIOLOGY OF THE SEASONS 



inferior in attractiveness or in stimulating power. If this is 

 not the case, the process of Sexual Selection does not work. 



It seems very important that we should get to know more 

 in regard to the correlation of the masculine or the feminine 

 characters. There is a growing body of evidence to show 

 that the secondary differences between males and females 

 hang together physiologically, and that a condition of their 

 development in the individual is an internal liberating 

 stimulus from the essential reproductive organs. The 

 secondary sex peculiarities, which we may sum up as mascu- 

 linity or femininity, are the manifold outcrops of the deep 

 primary constitutional difference which leads to maleness or 

 to femaleness, which makes of one animal an egg-producer 

 and of another a sperm-producer. A study of the hereditary 

 relation throughout the world of organisms leads to the idea 

 that every germ has a dual inheritance of masculine and of 

 feminine characteristics. One or other of these will find 

 expression in development, according as the germ develops 

 towards maleness or femaleness. What determines the sex 

 is a still more difficult question. 



Another useful idea has become clearer of late. It is now 

 generally believed that what the female chooses if she 

 chooses is not so much slight improvements in chirping or 

 song, slight excellences in colour or scent, but rather the 

 tout-ensemble of that male who most excites her sexual 

 interest. 



As Weismann says : " Even though we certainly cannot 

 assume that the females exercise a conscious choice of the 

 handsomest male, and deliberate, like judges in a Court of 

 Justice, over the perfections of their wooers, we have no 

 reason to doubt that distinctive forms (decorative feathers 

 and colours) have a particularly exciting effect upon the 

 female, just as certain odours have among animals of so 

 many different groups, including the butterflies," 



