so 



MOLLUSC A. 



With even such a portion of these facts as may be 

 observed by the naked eyes, without help of the micro- 

 scope or dissections, a child can be led to see at least 

 the parts of the animal, the work they do, and the rela- 

 tions of the shell to the animal ; and also that this is a 

 part of the oyster, and, though- a protective covering, 

 neither like a coat or a suit of armor or a house, or any 

 other artificial covering whatever. 



Such comparisons are misleading, and should be 

 made only where they are truly applicable, as in the 

 case of the hermit crabs, which seek protection in the 

 shells of dead mollusks and other similar instances. 



A very lively interest can be awakened by leading 

 children to observe the symmetrical distribution of the 

 parts in pairs, on either side of an imaginary plane 

 passed through the animal. 



If the oyster is held with the pointed end of the 

 shell away from them, the broader ends towards them, 

 the scholars will readily perceive that the mouth is at 

 one end of the body, the anus at the other ; the mantle 

 valves symmetrical, one on either side ; the palpi and 

 gills in pairs, and so on. They can be brought finally 

 to realize, that, although in many specimens twisted or 

 distorted until all external comeliness of shape is de- 

 stroyed, the shell is built by an animal with a definite 

 anterior, or forward end, where the mouth is always 

 to be found surrounded by its own peculiar organs for 

 feeding, and an equally well-defined posterior or hinder 

 end, where the terminus of the alimentary canal occurs 

 at the anal opening ; that this same soft-bodied creature 

 has also right and left symmetry to its body, like that 

 which we observe in man and all the higher animals ; 



