248 OKGAXS OF LITTLE IMPORTANCE [Chap. VI. 



of putrid matter ; but we should be very cautious in 

 drawing auv such inference, when we see that the skin 

 on the head of the clean-feeding male Turkey is likewise 

 naked. The sutures in the skulls of young mammals 

 have been advanced as a beautiful adaptation for aiding 

 parturition, and no doubt they facilitate, or may be 

 indispensable for this act; but as sutures occur in the 

 skulls of young birds and reptiles, which have only to 

 escape from a broken egg, we may infer that this 

 structure has arisen from the laws of growth, and has 

 been taken advantage of in the parturition of the higher 

 animals. 



We are profoundly ignorant of the cause of each 

 slight variation or individual difference : and we are 

 immediately made conscious of this by reflecting on the 

 differences between the breeds of our domesticated 

 animals in different countries, — more especially in the 

 less civilised countries where there has been but little 

 methodical selection. Animals kept by savages in 

 different countries often have to struggle for their own 

 subsistence, and are exposed to a certain extent to 

 natural selection, and individuals with slightly different 

 constitutions would succeed best under different 

 climates. With cattle susceptibility to the attacks 

 of ilies is correlated with colour, as is the liability to be 

 poisoned by certain plants ; so that even colour would 

 be thus subjected to the action of natural selection. 

 Some observers are convinced that a damp climate 

 affects the growth of the hair, and that with the hair 

 the horns are correlated. Mountain breeds always 

 differ from lowland breeds ; and a mountainous country 

 would probably affect the hind limbs from exercising 

 them more, and possibly even the form of the pelvis ; 



