MOLLUSCA. 5 



with what you know of other animals. First, 

 tell me some qualities that appear to you to be 

 common to all the mollusca. 



Child. Their bodies are soft, fleshy, moist, 

 and cold. 



Teacher. Yes, you remember their name is 

 given to them from their softness. Observe also 

 the action of a snail when you come near to it. 



Child. It draws its body into its shell for 

 protection. 



Teacher. Yes ; the bodies of the Mollusca 

 are contractile, that is, have a strong power of 

 contraction which they exercise by means of 

 muscles. What more do you remark in these 

 creatures ? 



Child. They have a thick skin which appears 

 loose in some of them. 



Teacher. This skin is called the sac or man- 

 tle ; and is peculiar to the molluscous tribe. It 

 is constantly moistened by a slimy exudation, and 

 is also full of pores and glands, of which I shall 

 have occasion to speak in a future lesson. What 

 are pores ? 



Child. Pores are very small holes. 



Teacher. What do you know about glands ? 



Child. I do not exactly know what glands 

 are ; but we have glands in our throats ; are 

 those of the mollusks the same as ours ? 



Teacher. They are of the same nature, but 

 much smaller than those in our throats. The 

 office of glands is to secrete or separate fluids of 



