HABITS AND FACULTIES. 6 



populous were covered with forests at no very distant period, and all 

 tlie terrestrial mollusks were then, like ours at the present time, living 

 in the forest. The progress of agriculture there was very slow com- 

 pared with its advances in this country, and thus time was given to the 

 animals to accustom themselves to the change ; and they have thus, by 

 slow degrees, adopted their present habits. 1 In the United States the 

 advance of agriculture in newly settled parts is very rapid ; large tracts 

 of forest are almost simultaneously subjected to the axe and to fire, and 

 a very few years produce an entire change in the vegetation of a whole 

 section. Consequently these animals are at once exterminated, or the 

 few that survive are brought suddenly under the influences of new cir- 

 cumstances, which, from the abruptness of the change, are fatal to them, 

 but which, if imposed upon them more gradually, might have been 

 sustained. A few spots and some limited tracts of land, remaining 

 unchanged in the midst of cultivation, protect some individuals of every 

 species ; and it is from this comparatively small number, thus preserved, 

 that their subsequent increase is derived. But at this period the field 

 is equally open for the multiplication of those foreign species which 

 accompany man as for the native species, and it is not surprising that 

 the former, whose habits are already adapted to the existing state of 

 things, should increase more rapidly than the latter. The native species, 

 however, become gradually familiarized with the circumstances around 

 them, and some few of them advance, and after a time establish them- 

 selves in the open country, where they seek such shelter as they can 

 find. This transition is very slow, but there are sufficient indications, 

 in the exceptions which are found to the general habits of the species in 

 this particular, to show that it is going on ; and therefore it is reason- 

 able to believe that when a period shall have elapsed as long as that 

 since the south and west of Europe were covered with forests, our species 

 will have become able to sustain themselves in the open country, and 

 will have spread themselves in great numbers over those populous parts 

 where they are now wanting. The power of adaptation to new circum- 

 stances, which is a prominent quality of nearly all the shell-bearing species 

 of this order, and which, combined with a remarkable tenacity of life, 

 enables them to resist successfully the many dangers to which they are 

 exposed, is illustrated in the extremes of their mode of life on the two 



1 I am not able to state whether the European snails are, as a class, similar in their 

 habits to Tachea hortensis, or whether many of them may not be restricted to the forests, 

 as ours are. 



