Natur^al History of Molluscous Animals, 39 



Art. X. All Introdtictio7i to the Natural History of Molluscous 

 Animals. In a Series of Letters. By G. J. 



Letter 3. Indirect and Direct Benefits, 

 Sir, 



In my last letter I illustrated, at some length, one grand 

 use of the Mollusca in the economy of nature : that, viz., of 

 furnishing sustenance to many animals. But you will observe 

 that a vast number of the class are themselves carnivorous, 

 and become thus a means, in the hand of Providence, of keep- 

 ing in check the multiplication of the tribes on vrhich they 

 prey, and of preserving between them that due proportion and 

 " balance of power" which is as necessary in the animal, as in 

 the political, world. Others, again, are gifted with the remark- 

 able property of boring through stone and wood, and thus 

 reduce to dust the rock over which the waves might have 

 broken in vain, and remove those forests which the torrents 

 and tornadoes of tropical climes annually float to the feea. In 

 this sense, even the " fell Teredo" ministers to good. " The 

 seaman," to adopt the rather pompous language of a very ex- 

 cellent author, "as he beholds the ruin before him, vents his 

 spleen against the little tribes that have produced it, and 

 denounces them as the most mischievous vermin in the ocean. 

 But a tornado arises, the strength of the whirlwind is abroad, 

 the clouds pour down a deluge over the mountains, and 

 whole forests fall prostrate before its fury. Down rolls the 

 gathering wreck towards the deep, and blocks up the mouth 

 of that very creek the seaman has entered, and where he now 

 finds himself in a state of captivity. How shall he extricate 

 himself from his imprisonment ? an imprisonment as rigid as 

 that of the Baltic in the winter season. But the hosts of the 

 Teredo are in motion : thousands of little augers are applied 

 to the floating barrier, and attack it in every direction. It is 

 perforated, it is lightened, it becomes weak ; it is dispersed, or 

 precipitated to the bottom ; and what man could not effect, is 

 the work of a worm. Thus it is that nothing is made in vain ; 

 and that, in physics, as well as in morals, although evil is 

 intermingled with good, the good ever maintains a predomi- 

 nancy." * 



The conversion, through their agency, of other materials 

 into lime, seems, however, to be the great purport of the cre- 

 ation of molluscous animals. Shells consist of carbonate of 

 lime with a greater or less proportion of animal matter, and 

 the animals form these shells from their food, which contains 



. * Good's Book of Nature, vol. i. p. ^65. 

 D 4? 



