ON MOLILUSCA. 203 
slightest solidity. Accordingly, it is probable that they feed 
upon animal and perhaps vegetable particles, the result of the 
decomposition of the beings of either of these kingdoms, and 
which are drawn along with the fluid which enters into the 
cavity of the mouth for respiration. It might also happen 
that their nutriment is composed of the innumerable animal- 
cule which the microscope enables us to observe in the water 
where these animals live, and which are of an extreme soft- 
ness. The nucule may perhaps feed on substances of greater 
solidity, as might be supposed from the disposition of their 
labial appendages. 
According to the nature of the aliment, and the state in 
which they seize it, it is evident that the means which the 
mollusca employ to take it must be very different. 
Species, such as the brachiocephala, and even the testacellz, 
which feed upon living fugitive prey, are obliged either to pur- 
sue it when they have the means, as the sepiz and loligines, 
or to wait in ambuscade and cast themselves suddenly upon it. 
This is the case with the octopi, and probably with the testa- 
cella. 
Those which, on the contrary, feed on living animals, but 
immoveable, attach themselves upon them, pierce their en- 
velopes, of whatever nature they may be, by the assistance 
of the hooks with which their proboscis is armed, and conse- 
quently have but little difficulty in finding their prey, which 
is generally incapable of all sort of motion. 
The mollusca which feed on animal or vegetable substances 
in a state of decomposition, seek them, without doubt, guided 
essentially by the smell, and have need of no great efforts 
to obtain them. 
There are even some among those which, like the greater 
portion of the limacinz, compose their aliment of living vege- 
table substances, more or less solid. ‘They have only to seek 
them out, and cut them into small pieces. 
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