MILESTONES OF EVOLUTION 51 



days there lived at any rate two species which were clad in 

 long, shaggy coats, and these, too, roamed over what 

 now form the British Islands. The one we know as the 

 Mammoth, the other as the woolly rhinoceros. 



From this we may regard it as fairly certain that of 

 the many species of elephants and rhinoceroses which have 

 become extinct all were more or less hairy. In the woolly 

 species the hair had become lengthened, in adaptation to 

 the requirements of a cold climate, or at any rate of a 

 climate characterised by long and severe winters. 



The hedgehog, when newly born, is blind and naked ; 

 later a hairy coat appears, the hairs on the upper part of 

 the body being white and flattened. These soon develop 

 into the spines characteristic of the adult. Here we get an 

 insight into the origin of the spines, and the repetition of 

 ancestral characters. This history is the more interesting, 

 because in the tenrec of Madagascar, another member of 

 the same great family, the Insectivora, we have a reversal 

 of this process. Young tenrecs have an armature of 

 strong white spines arranged in longitudinal lines along 

 the back, but before the adult stage is attained the spines 

 are shed and succeeded by a crest of long, stiff hairs, 

 from which we may infer that the more remote ancestors 

 of this animal were armed with spines. And this infer- 

 ence is materially strengthened by the fact that in two 

 nearly related species — the half-spined and black-headed 

 tenrecs, these spines are retained throughout life ; while 

 in yet another species, the hedgehog tenrec (Ericulus 

 setosus) the spiny armature has increased, covering the 

 whole of the upper surface of the body as in the true 

 hedgehog. 



We might add considerably to the number of instances 

 of this kind, but let two more suffice. The " Eared-seals " 



