MOLLUSCA. 5 



parts and habits, 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 con- 

 traction 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 aslimy 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 

 various kinds from the general fluid of the sub- 



