310 THE COURTSHIP OF ANIMALS 



colours, or of " warning coloration," as circumstances 

 may demand. There is nothing more remarkable in 

 this than the control which the pituitary body exercises 

 over stature, either when in a pathological condition, 

 or when the controlling action of the other gland secretions 

 is removed, as by castration. 



Hitherto much has been made of trophic nerves, which 

 control growth ; but it is probable we have overlooked 

 the still more important action of " trophic " glands, 

 such as the thyroid.^ This apparently controls growth 

 in many directions. Adaptations to environment which 

 ire effected by changes in bodily shape — as in the trans- 

 formation of land-dwelling mammals into Seals and 

 Whales — are probably largely controlled by these glands. 

 Their activity is as great as their manifestation is varied. 



Why their action should be more stimulating in the 

 case of the male, why he should lead the way in all the 

 new acquirements of the species, both in non-sexual as 

 well as in sexual characters, is by no means plain. But 

 the fact remains that this is so. Remove any one of these 

 glands and the machinery of growth is thrown out of 

 gear; it is not merely the secondary sexual characters 

 which are affected. 



• But these glands are concerned no less intimately with 

 tne behaviour of animals. This is most obvious in all 

 that concerns sexual appetite as the preceding chapters 

 have already shown. Having regard to the immense 

 variety of animals concerned, this behaviour presents an 

 underlying uniformity of expression which must not be 

 lost sight of : and the same is no less true of what we may 

 call the physical manifestations of these glandular activities. 



THE END 



