348 SUPPLEMENT 
creep sufficiently fast by the assistance of the very broad 
muscular disk with which they are provided, not only over 
solid bodies, immerged or not, but also at the surface of the 
water. In this case they are inverted, the shell beimg below 
and the foot above. It appears that the contraction of the 
foot takes its hold of a very light stratum of the water, which 
they leave above them. Their strength, however, cannot be 
very great, and in fact the slightest wind is often sufficient to 
accumulate the limnee, thus floating towards the opposite 
side from which it blows. On the least danger, they with- 
draw all their parts into the shell, become of a greater specific 
weight, and fall to the bottom. To return to the surface they 
are obliged to crawl along the bottom, as far as the bank, or 
to follow the stem of some aquatic plant. It is only in the 
water, and in the fresh water especially, that the limnee are 
to be found, and as this fluid cannot serve them for respiration, 
they are obliged to come from time to time to the surface to 
respire the atmospheric air. Sometimes they are found alto- 
gether out of the water, but on some aquatic plant, and never 
even at the slightest distance from the element. They feed on 
vegetable substances alone, and especially on the leaves of 
aquatic plants, which they cut, like the slugs, with the tooth 
with which their mouth is armed. During winter, at least in 
our climates, they fall into a sort of torpor, and sink more or 
less deeply into the mud which is at the bottom of the ponds, 
marshes, rivers, or streams, that they inhabit. It is at the 
end of spring, when their activity becoms greater, that they 
engage in the grand work of reproduction. Although her- 
maphrodites, their mode of intercourse differs from that of 
the limaces and helices ; for with the limnzz the concourse of 
three individuals is necessary, and as others come up, they 
thus form long cordons. At the end of a certain time after 
this, of the duration of which we are ignorant, the fecundated 
individuals deposit upon dead or living bodies in the water, 
2 
5 
d 
4 
