242 FROM THE GREEKS TO DARWIN 



I conceive that a Gasteropod mollusc, which, as it 

 crawls along, finds the need of feeling the bodies in 

 front of it, makes efforts to touch those bodies with 

 some of the foremost parts of the head, and sends to 

 these every time quantities of nervous fluids, as well 

 as of other liquids ; I conceive, I say, that it must re- 

 sult from this reiterated afflux toward 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 same animal 

 flow also to the same places, and especially nourish- 

 ing fluids, it must follow that two or four tentacles 

 will appear and develop insensibly under those cir- 

 cumstances, on the points referred to. 



As illustrating the sensitiveness of lowly or- 

 ganized animals to the action of environment, he 

 cites a series of his observations upon the primi- 

 tive fresh-water Hydra when moving about in 

 search of light. 



Numerous other examples are given of the 

 supposed origin of other parts of the body, 

 among which we may summarize his hypothesis 

 of the evolution of mammals and of the origin of 

 the hoof in mammals:^ 



All mammals sprang from saurians, more or less 

 similar to our crocodiles. They first appeared under 

 the form of amphibian mammals with four feebly de- 

 veloped limbs. These primitive forms divided in the 

 manner according to which they fed. Some, accus- 

 toming themselves to browse upon shrubs, became the 



^Philosophie Zoologique, 1873, vol. I, pp. 252-3; vol. II, pp. 

 418-423. 



