EVOLUTIONS OF ORGANIZATION. 13 



The proofs of the effect of new wants or appe- 

 tency, in producing new organs, he derives from 

 the acknowledged effect of habitual action in in- 

 creasing the development of organs. But while it is 

 difficult to limit the results of use, disuse, or peculiar 

 action in developing, dwindling, or modifying struc- 

 tures already in some form existing, it is not easy 

 to understand how such a principle could operate 

 to produce an organ the basis of which was not 

 previously laid down. 



That which gives the air of absurdity to Lamarck's 

 illustrations is that, altogether unlike St. Hilaire, he 

 appears to have ignored the necessity for a prin- 

 ciple independent of external circumstances to regu- 

 late form, in, for example, such matters as symmetry. 

 The following may be given as an instance : "I 

 conceive that a gasteropod mollusc, which, as it 

 crawls along, finds the need of touching the bodies 

 in front of it, makes efforts to touch those bodies 

 with some of the foremost parts of its head, and 

 sends to these every time quantities of nervous 

 fluids, as well as other liquids. I conceive, I say, 

 that it must result from this reiterated afflux towards 

 the points in question that the nerves which abut 

 at these points will, by slow degrees, be extended. 

 Now, as in the same circumstances other fluids of 

 the animal flow also to the same places, and espe- 



