MOLLUSCA. 23 



LESSON IV. 



(Before proceeding to the study of Shells, there should be a 

 recapitulation of all the children have learnt concerning the 

 animals, and a summary read to them and written down by 

 them from recollection. ) 



The mollusks have a soft, cold, slimy, and 

 contractile body moved hy muscles. They have 

 no articulated moveable parts as limbs ; in some, 

 the organs of motion are tentacula of different 

 forms ; in others, a fleshy foot extending along 

 the underpart of their bodies ; this fleshy sub- 

 stance is sometimes free and pliable, and can be 

 projected and drawn in at pleasure. The bodies 

 of the mollusks are enveloped in a sac or mantle 

 of skin full of pores and glands, which some- 

 times spreads over their shell. They are desti- 

 tute of bones. They have not red warm blood, 

 but a white cold fluid circulates through their 

 frames in vessels issuing from a heart. They 

 have nerves connected with their different organs. 

 They are divided into two classes. The first, 

 mollusca cephala, have a distinct head, bearing 

 lips or jaws, and are furnished with eyes and 

 tentacula. The second, mollusca acephala, have 

 a more simple organization ; they have no dis- 

 tinct head, and are destitute of jaws and other 

 hard parts of a mouth ; they inhabit shells 

 formed of two pieces. 



