304 EVOLUTION, OLD AND NEW. 



" Even in the lifetime of a single individual we can 

 see organic changes in consequence of changed habits. 

 Thus M. Tenon has constantly found the intestinal 

 canal of drunkards to be greatly shorter than that of 

 people who do not drink. This is due to the fact that 

 habitual drunkards eat but little solid food, so that 

 the stomach and intestines are more rarely distended. 

 The same applies to people who lead studious and 

 sedentary lives. The stomachs of such persons and of 

 drunkards have little power, and a small quantity will 

 fill them, while those of men who take plenty of exer- 

 cise remain in full vigour and are even increased." * 



It becomes now necessary to establish the converse 

 proposition, namely that : 



" The frequent use of an organ increases its pou-er ; it 

 even develops the organ itself, and makes it acquire dimen- 

 sions and powers which it is not found to have in animals 

 which make no use of such an organ. 



" In support of this we see that the bird whose needs 

 lead it to the water, in which to find its prey, extends 

 the toes of its feet when it wants to strike the water, 

 and move itself upon the surface. The skin at the 

 base of the toes of such a bird contracts the habit of 

 extending itself from continual practice. To this cause, 

 in the course of time, must be attributed the wide 

 membrane which unites the toes of ducks, geese, &c. 

 The same efforts to swim, that is to say, to push the 

 water for the purpose of moving itself forward, has ex- 

 tended the membrane between the toes of frogs, turtles, 

 the otter, and the beaver." f 



* Phil. ZooL,' tow. i. p. 247. f Page 248. 



