Natural History 461 



5 



Subterranean Mammals 



As life on the surface of the earth is attended by great 

 risks, which have to be met by special adaptations, it is not sur- 

 prising that many mammals should seek refuge underground or 

 should combine terrestrial and subterranean habits. Of adapta- 

 tions to thoroughgoing subterranean life the Mole is perhaps 

 the finest instance. Its hand is turned into a strong shovel, with 

 which it literally "swims" in the earth. To the inside of the 

 thumb there is a special sickle bone, which broadens the digging 

 surface. The breast muscles are like an athlete's, and those of 

 the very short neck are well suited for tossing the earth. There 

 are no projecting ear-trumpets, for these would be much in the 

 way; the eye, unnecessary in darkness, is reduced to a pin-head 

 size (1-25 of an inch in diameter), and is protected from injury 

 by being well hidden in the hair of the head; the position of the 

 nostril rather under the tip of the snout and a lip-fold in front 

 of the mouth serve to keep the earth out; the hair of the body 

 has no "set" and is easily kept clean, moreover it does not get 

 disordered when the burrower moves backwards; the crowns of 

 the back teeth are covered with sharp cusps, most admirably 

 suited for crunching insect larva? and the like. Truly the Mole 

 is a bundle of adaptations. The Common Mole burrows in soft 

 soil, and its hand is therefore broad; but the Cape Golden Mole 

 and the quite unrelated "Marsupial Mole" burrow in hard soil, 

 and their hands are very narrow, with a great strengthening of 

 two of the fingers. This is plainly as it should be, and the 

 impression of fitness grows when we consider details. Thus the 

 Marsupial Mole, which presses its head into the earth, has its 

 neck vertebrae solidified. 



The Mole 



We have mentioned the Mole's adaptation to subterranean 

 life, but this extraordinarily interesting mammal claims further 



