228 ANIMALS UNDERGROUND 



common moles, tuco-tuco, and the marsupial sand-moles, 

 which obtain their food below the earth-surface as 

 diving birds catch fish below the sea-surface. It is 

 almost an inversion of their normal way of life, and is 

 probably due to some such compulsion as has also 

 forced many animals ' to become nocturnal. Nor is it 

 doubtful that if once this necessity were removed, their 

 tendency would be to abandon this unnatural life, and 

 return to the regions of light. How strong the pressure 

 must have been which forced them underground may be 

 gathered from the list of English terrestrial mammals. 

 Twelve of these are bats ; but of the remaining twenty- 

 nine no less than sixteen, or more than half, live either 

 wholly or partly underground. The list includes the 

 fox, three shrews, the mole, the badger, the otter, three 

 species of mice, two rats, three voles, and the rabbit. 

 Besides there are several species of birds, as widely 

 different in habit as the stormy petrel, sand-martin, 

 puffin, sheldrake duck, and kingfisher, which for a 

 time live in holes excavated in the earth. To abandon 

 the sun, to bask in whose rays is to most animals one 

 of the most agreeable of physical enjoyments, is an 

 almost greater sacrifice than the relinquishment of fresh 

 air. Yet the sacrifice is made, and the creatures, though 

 not without occasional suffering and loss of health 

 directly attributable to this cause, have succeeded in 

 adapting themselves with great success to the new con- 





