MOLLUSCA. 89 



CHAPTER m. 

 MOLLUSCA: THEIR SHELLS, TONGUES, EYES, AND EARS. 



ONE of the most interesting aspects of microscopic study 

 is that in which it reveals the intimate structure of objects, 

 which, to the unassisted eye, appear simple or nearly so, 

 but which prove by the aid of magnifying power to be 

 complex. Thus we are often introduced to very curious 

 contrivances (if I may use such a word in reference to the 

 works of God), by which difficulties are overcome, and 

 substances, which would seem at first wholly unfit for 

 certain duties, are in the most admirable manner adapted 

 to fulfil them. 



The combination of strength and lightness is always a 

 difficult problem in human art; its successful solution 

 always excites our admiration. In the Divine mechanics, 

 too, it is very often required, and the variety of modes in 

 which it is accomplished are in the highest degree novel 

 and suggestive. We lately saw one of these in the struc- 

 ture of a feather, in the contrivance by which extreme 

 lightness of material was made, by a most remarkable 

 arrangement, to ofier a firm resistance to opposing force. 

 I have now another example to show you, in which a 

 material, in itself heavy, is by its arrangement made very 

 light, while it preserves its strength. 



You have seen many times, when walking along the 

 yellow sands kissed by the rippling waves, the shell, or 

 bone, as it is sometimes called, of the Cuttle-fish. You 

 know that it consists of a shallow boat-shaped shell, the 

 hollow of which is filled with a white substance, which can 



