22 LESSON III. 



a without, and K<paXy 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 organi- 

 zation altogether is much more simple than that 

 of the mollusca cephala. They are aquatic ani- 

 mals, 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 scollop, 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 

 mollusca, 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 terminated by a cartilaginous border, fur- 

 nished 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 

 contains 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. 



