22 LESSON III. 



a without, and Ace^aX^ a head. The mollusca 

 acephala have not a distinct head, nor any ap- 

 pearance of the organs of sight or hearing, their 

 mouth is only a simple opening, and their or- 

 ganization altogether is much more simple than 

 that of the mollusca cephala. They are aquatic 

 animals, and their shell is composed of two pieces, 

 to which they are attached by muscles. Which 

 of these mollusks would you place in this class ? 



Child. The oyster, the scallop, and the muscle. 



Teacher. Here is the summary of to-day's 

 lesson ; read it carefully, and then take pains 

 to write me a correct account of it. 



The organs of nutrition possessed by the mol- 

 lusca, vary according to their habits. Those 

 which feed on vegetables, have a muzzle com- 

 posed of horny jaws sometimes armed with teeth. 

 Many of the carnivorous mollusca, have a fleshy, 

 pliable proboscis, moved by muscles, and ter- 

 minated by a cartilaginous border, furnished 

 with teeth ; others have only a simple opening, 

 and possess no organ of mastication. The 

 mollusca are divided into two great classes ; one 

 contains those animals possessing a head, which 

 are called mollusca cephala, the other con- 

 tains those which are destitute of a head, and 

 are called mollusca acephala. The latter are 

 distinguished by a much more simple organi- 

 zation, live invariably in water, and inhabit 

 shells composed of two pieces. 



