144 THE COURTSHIP OF ANIMALS 



all habited in the same vivid hues. There are infinite 

 variations of these changes which cannot be discussed 

 here, for obvious reasons. All that matters now is the fact 

 of such sequences, which inevit.-ibly raise the questions : 

 Why, in so many cases, do the females show no disposi- 

 tion to assume resplendent colours ? And to what factors 

 can such coloration, when it occurs, be attributed ? The 

 second only of these questions is germane to the present 

 discussion, and to this no very satisfactory answer can 

 be returned. 



To say that the development of brilliance in species 

 hitherto sombrely clad is due to " changes in the meta- 

 bolism " is only an affectation of wisdom. What we 

 want to know is what induces the changes ? Time was 

 when no more than a guess could be hazarded as to this : 

 a suggestion that ornament, of whatever kind, was one 

 of the many modes of the expression of that instability 

 of the organism which is characteristic of living things : 

 that it was one of the outward and visible signs of that 

 inward, intangible tendency to vary which is so familiar. 

 Later research seemed to show, fairly conclusively, that 

 ornament was one of those " secondary sexual characters " 

 which was dependent on the stimulating juices, or 

 " hormones," emanating from the primary sexual glands. 

 To-day it is manifest that this is only partly true, for it is 

 certain that these glands are not alone concerned and 

 they may only participate indirectly. It seems to have 

 been clearly demonstrated that the thyroid and pituitary 

 glands, or the " hormones " therefrom, play a large part in 

 this matter of the " secondary sexual characters." 



Castration, it is true, profoundly affects these characters. 

 In the case of Deer it inhibits the growth of antlers, 

 in Cattle the horns are increased in length but reduced 



