MOLLUSC A: THEIR SHELLS 63 



CHAPTER III 

 MOLLUSCA: THEIR SHELLS, TONGUES, EYES, AND BARS 



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 diffi- 

 culties 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 al- 

 ways 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 

 structure of a feather, in the contrivance by which ex- 

 treme lightness of material was made, by a most remark- 

 able arrangement, to offer 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 aggregate 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, 



