50 Our Food Mollusks 



of it. It was the irony of fate that the lasting benefit 

 of his labor was to natural science, the deadly foe of 

 theology, by fixing in the mind of the thinking world, as 

 nothing else had done, knowledge concerning the utilities 

 of mechanisms, the usefulness of parts, and the adaptation 

 of the whole organism to its environment — foundation 

 facts in Darwin's explanation of the origin of species by 

 natural selection. 



So it has happened that the structure and operation of 

 mechanisms in animal and plant bodies have received 

 much attention from biologists, and have often excited 

 great admiration for the complexities and beauties of 

 their adjustments. Illustrations of mechanisms may be 

 had from any group of organisms, though the more in- 

 tricate ones are to be found, as might be expected, in 

 the bodies of higher animals or plants. 



They are often very complicated, however, in more 

 lowly forms. Judging from the jocular references to 

 the placidity of the oyster and the happiness of the clam 

 that no popular writer has ever been able to avoid when 

 mentioning them, the common notion seems to be that 

 these are inert, structureless, functionless masses of pulp, 

 living the simple life reduced to its lowest possible terms. 

 But in the chapter on anatomy, it was shown that a semi- 

 automatic ciliary mechanism exists in the members of the 

 bivalve group for straining food particles out of the 

 water and passing them to the mouth. That such a 

 function was performed, has been known for a long time, 

 but it was first observed by the writer that there exists 

 in connection with it another and even more complicated 

 mechanism, depending largely on the nervous system for 

 its operation, by means of which mud and other useless 

 matter collected by the gills may be carried away from 



