334 SUPPLEMENT 
the earth. It is at the end of autumn that the snails thus 
retire. During the whole of the fine season, they do not 
re-enter into the excavations which conceal them, except 
during the heat of the day, and particularly in dry weather ; 
for as soon as rain falls, and especially in fine and gentle 
showers, they may be seen to issue forth from all parts, as 
they commonly do during the night. ‘Their mode of locomo- 
tion, which may easily be observed by placing one of these 
animals in a transparent body, is a peculiar kind of reptation, 
in which the animal seems to glide on the plane which sup- 
ports it, and to follow all its irregularities. But on closer 
examination, we find that this reptation is executed by means 
of the successive action of all the ranks of little muscular 
fibres of which the inferior face of the body is composed, 
something the same as in certain articulated animals, in 
which the number of articulations is very considerable. Al- 
though this mode of locomotion is very slow, yet the snails 
do not fail to advance more than one would imagine at first 
sight. As their resting point is always taken in front, it is 
always in this direction that they draw themselves along, and 
never backwards. ‘The mucous matter which issues from all 
the parts of these animals, but especially from the foot, and 
which enables them to adhere more strongly even to the 
smoothest bodies, remains on the surface of these bodies, and 
through desiccation, which is very prompt, leaves a sort of 
silvery trace, which always betrays the route which these 
animals have taken. It is this matter which forms the 
epiphragma, as it is that which exudes from all parts of the 
skin, covering the visceral mass, and especially from the edges 
of the mantle, or collar, that produces the shell. No helices 
have been seen able to swim, or even crawl in an inverted 
posture on the surface of the water, as the lymnez, and some 
neighbouring genera can do. It is generally in search of their 
food, or of some individual of their own species, during the 
——_——- se 
