1 4 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 taste 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 



