ZO LESSON III. 



without, and K^aAi? a head. Jhe mollusca ace- 

 phala have no distinct head, nor any appear- 

 ance either of the organs of sight or hearing ; 

 their mouth is only a simple opening for the 

 reception of their food. They all inhabit the 

 water. Their shells are composed of two pieces 

 united by a hinge, and the animals are attached 

 to them by muscles which pass through their 

 bodies, and by means of which they open and 

 shut them. Many of the species have no power 

 of locomotion, and their organization is alto- 

 gether very inferior to the mollusca cephala. 

 Do you remember any instances of this class ? 



Child. The oyster and the muscle must 

 belong to the mollusca acephala. 



Teacher. Yes. You must now endeavour to 

 recollect all that we have said about the mol- 

 lusca. I will arrange the matter, and write it on 

 the slate, and you shall afterwards commit it to 

 memory. 



Mollusca. 



The mollusca have a soft, cold, slimy, and 

 contractile body moved by muscles. They have 

 no articulated moveable parts as limbs ; the prin- 

 cipal organs of motion are tentacula of different 

 forms, and answering various purposes. Some 

 have a fleshy foot extending along the under par t 

 of their bodies ; in others the fleshy substance is 

 free and pliable, and can be projected and drawn 

 in at pleasure. Their bodies are enveloped in 

 a sac or mantle of skin, full of pores and glands, 

 which sometimes spreads over their shell. They 



