MOLLTJSCA. 43 



OHAPTEE m. 



MOLLUSOA : THEIR SHELLS, TONGUES, ETES, AND EAES. 



Oira; 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 proYe, by the aid of magnifying 

 power, to be complex. Thus we are often introduced to 

 very curious coni/rivances (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 admira- 

 ble 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 mechan- 

 ics, 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 extreme lightness of material was made, by 

 a most remarkable arrangement, to offer a firm resis- 

 tance 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 



