14 MOLLUSCA. 
only, namely the cuttle-fish, the rudiments of the organs of 
hearing have been detected. The organs adapted to smell- 
ing cannot be exhibited, but the existence of the sense is 
demonstrated by the facility with which molluscous animals 
discover suitable food, when placed within their reach. 
The sense of ¢aste appears to exist, but it is difficult to point 
out the particular parts of the mouth fitted for its residence. 
As, however, particular articles of food are selected in pre- 
ference to others, it may be concluded from analogy that 
taste regulates the choice. 
In the classification of the mollusca, the characters fur- 
nished by the nervous system, from the difficulty of their 
detection and exhibition, have never come into use. But 
those furnished by the organs of preception are highly priz- 
ed. Of these, the eye is the most obvious and constant. 
It varies in position in different species ; but, among indi- 
viduals of the same species its characters are constant. 
In the cutaneous, muscular, and nervous systems, traces 
of a general plan may be observed, according to which they 
have been constructed in the different tribes. In the or- 
gans which remain to be considered, there is less uniformity 
of structure, each family almost being constructed accord- 
ing to a model of its own. 
The time when molluscous animals feed has not been 
carefully attended to. Those which live in the water are 
beyond the reach of accurate observation. Those that re- 
side on land usually shun the light, and creep forth in the 
evenings to commit their depredations. During warm, dry 
weather, they stir not from their holes. | 
The animals under consideration, feed equally on the 
products of the vegetable and animal kingdom. Those . 
which are phytivorous appear to prefer living vegetables, and 
