4 TERRESTRIAL AIR-BREATHING MOLLUSKS. 



continents. We know of no other instances of animals living in a natural 

 condition, not domesticated nor accompanying man, where the same 

 diversity of habitat in analogous species exists. The presumption of 

 changes which shall approximate the habits of both, in proportion as 

 the physical circumstances of both approach each other, is therefore not 

 a violent one. But it is by no means certain that all the species will 

 survive the violent change to which they are at first exposed. Those 

 of them which are in a state of decline and nearly run out, and those 

 which are strictly local in their habitats, will be least able to sustain 

 themselves, and their entire extinction will be very likely to follow. 



All the species are nocturnal or semi-nocturnal in their habits. In 

 the daytime they seek such shelter as may be at hand, and retreat into 

 dark holes and crevices, or hide themselves under the fallen trunks of 

 trees, fragments of wood, leaves, and stones, or bury themselves wholly 

 or partially in the earth. There they remain inactive until evening 

 twilight, when, except in seasons of drought, they sally forth in num- 

 bers ; and in favorable situations, such as ravines and low places in the 

 forest, may be seen crawling over the surface of the ground, and some- 

 times climbing the stalks of plants and the trunks of trees. They are 

 probably active during the whole night, in which time they all seek 

 their food, and those species which are noxious to man commit their 

 depredations in the garden and orchard. At this time, too, their sexual 

 meetings take place. Soon after daylight they retire to their retreats, 

 and remain very close until night approaches again. They also come 

 forth when the atmosphere is charged with moisture, and after light 

 showers. 



There is a difference in the places of their retreat. The naked genera 

 are oftenest found attached to the lower surface of wood and stones 

 lying in contact with the ground, or to the damp walls of cellars, and, 

 in the forest, concealed under logs. So soon as, from the increased dry- 

 ness of the atmosphere, these places no longer retain moisture, they 

 abandon them for others, and in seasons of drought they penetrate 

 deeply into the earth. The shell-bearing genera, in the forest, are 

 observed under prostrate timber, to the lower surface and crevices of 

 which they adhere by a mucous attachment during the day, in hollows 

 under the roots of trees, and under the layer of decaying leaves which 

 cover the ground. In situations where such places of shelter are not 

 found, they half bury themselves in the soil, at the roots and under the 

 shade of thick tufts of plants. Numbers frequently resort to the same 



