INTRODUCTION. XVll 



coat, than the adult animals. The Mongolian Tiger is 

 a good example. Others, such as the Phocidae, or Hair- 

 Seals, are only thickly-furred when quite young, losing 

 the thick and woolly covering when they enter the 

 water. 



Size. 



As the wild animals decrease gradually in colour 

 towards the Poles, so they increase in size. This is a 

 very natural effect, for in a more northern and colder 

 latitude, animals have a great range of country to 

 traverse in order to procure their necessary food, thus 

 developing bone and muscle, and causing interbreeding 

 of the species. Moreover, the elimination of the more 

 weakly animals through rigour of climate, and the 

 consequent greater abundance of food for those remain- 

 ing, are causes likely to increase the size. Notable 

 examples are the White Hare, Beaver, Eed Fox, Skunk, 

 Eabbit, Bay Lynx, and Tiger. The Sitka Musk-rat is 

 a curious exception, which is difficult to account for, 

 unless by reason of scarcity of food in this district. 



The size of all animals is also increased by domesti- 

 cation. This is effected by crossing the various strains, 

 and is intensified by judicious high feeding. The 

 domestic Eabbit, and many breeds of cattle are cases 

 in point. In-breeding makes the stock become more 

 symmetrical, but smaller, and if carried to too great an 

 extent, sterility ensues. 



