HABITS AND FACULTIES. 5 



retreat, but this in tlie shell-bearing genera seems a mere matter of 

 accident, while in the introduced species of Limaces it appears to indi- 

 cate a gregarious habit, as they prefer to crowd together and lie in close 

 contact with and upon each other.^ These last are said by some to 

 occupy permanently the same retreat, but the assertion is probably 

 incorrect. They often, and perhaps generally, remain in the immediate 

 vicinity of the place where they procure their food, and hence they often 

 resort to the same place of shelter ; and as many of them have fre- 

 quently been observed in the same place, they have been thought to be 

 the same individuals. But when one set of individuals is destroyed, 

 another soon takes their place, and whenever a new shelter is provided, 

 by the accidental presence of fragments of wood in suitable situations, 

 it is immediately resorted to by them. The native genus Tehennophorus 

 is in no manner gregarious ; it lives in the forest, mostly buried in 

 decaying and rotten wood, and no more than two are usually found 

 together. In cloudy weather, Avhen the atmosphere is charged with 

 moisture, and during light showers, all the species come forth in the 

 daytime ; but on a change of weather immediately return again, and 

 during rains remain in their retreats. Long-continued or excessive 

 rains, however, inundate their hiding-places, drive them out, and force 

 them to resort to trees. 



We have seen, in a preceding part of this work,^ how numerous are 

 the agencies which are continually tending to destroy the lives of indi- 

 viduals, and to exterminate whole species. Being all of them slow in 

 their motions, without means of escape from enemies, destitute of instru- 

 ments of offence or of defence, and some of them unprovided with a cov- 

 ering, it would seem as if their existence must be very precarious, and 

 that they must be easy victims to the unfavorable circumstances around 

 them. Such would be the case undoubtedly, and these causes would 

 interfere with the diffusion of species and derange their distribution in 

 a greater degree than they actually do, if there were not counteracting 

 properties in the animals themselves which modify and limit the destruc- 

 tive tendency. These conservative properties are, their prolific gener- 

 ative capacity, their insensibility to pain, their extreme tenacity of life, 

 and their extraordinary power of reproducing important organs which 

 have been cut off or destroyed by accident. 



1 The promiscuous mingling of individuals of Limax agrestis and Limax variegatus in 

 their respective retreats has often reminded us of the familiar positions in which swina 

 place themselves for sleep. 



2 See I. 132 et seq. 



