DWELLINGS 1607 



resembles a very small crab. But his inveterate habit 

 during so many generations of sheltering his abdo- 

 men in a shell prevents this part from being incrusted 

 with lime and becoming hard. The legs and the head 

 remain in the ordinary condition outside the house, 

 and the animal moves bearing it everywhere with 

 him; on the least warning he retires into it entirely. 

 But the crustacean grows. When young he had 

 chosen a small shell. A mollusk, in growing, makes 

 his house grow with him. The hermit-crab can not 

 do this, and when his dwelling has become too nar- 

 row he abandons it for one that is more comfortable. 

 At first inclosed in the remains of a Trochus, he 

 changes into that of a Purpura; a little later he seeks 

 asylum in a whelk. Besides the shelter which these 

 shells assure to the crustacean, they serve to mask 

 his ferocity, and the prey, which approaches confi- 

 dently what it takes to be an inoffensive mollusk, be- 

 comes his victim. 



The great horned owl likewise does not construct 

 a nest, but takes possession of the dwellings aban- 

 doned by others. These birds utilize for laying their 

 eggs sometimes the nest of a crow or a dove, some- 

 times the lair which a squirrel had considered too 

 dilapidated. The female, without troubling about 

 the bad state of these ruins, or taking pains to repair 

 them, lays her eggs here and sits on them. 



It is time to turn to animals who have more regard 

 for comfort, and who erect dwellings for themselves 

 or their offspring. These dwellings may be divided 

 into three groups : ( i ) Those which are hollowed in 

 earth or in wood; (2) those which in the simplest 



