384 THE STUDY OF ANIMAL LIFE CHAP. 



dition of dwarfing was the restricted area for exercise. 

 (3) The results of physical exercises show that the size 

 and strength of a muscle may be greatly increased by 

 persistent practice. This is well known in the legs of 

 professional dancers, in the powerful wrist of the violinist, 

 and in the arms of the blacksmith. A force de forger on 

 devient forger on. 



Even if we could gather many illustrations of the 

 influence of use and disuse on individual animals, we 

 should still have to find out whether the peculiarities or 

 modifications acquired by individuals were in any repre- 

 sentative way transmissible to the offspring, or whether 

 any secondary effects of the acquired characters were 

 transmissible, or whether these changes had no effect 

 upon succeeding generations. 



It is easy to find hundreds of cases in which the constant 

 characters of animals may be hypothetically interpreted 

 as the result of use or disuse. Is the torpedo-like shape of 

 swift swimmers due to their rapid motion through the 

 water, do burrowing animals necessarily become worm- 

 like, has the giraffe lengthened its neck by stretching it, 

 have hoofs -been developed by running on hard ground, 

 are horns responses to butting, are diverse shapes of 

 teeth the results of chewing diverse kinds of food, are 

 cave-animals blind because they have ceased to use their 

 eyes, do the wing bones and muscles of the domesticated 

 duck compare unfavourably with those of the wild duck 

 because the habit of sustained flight has been lost by the 

 former ? 



To questions of this sort it must be answered that the 

 facts at present known do not afford much support to 

 the theory of the direct origin of adaptations. "It is 

 infinitely easy," Semper says, ' to form a fanciful idea 

 as to how this or that may be hypothetically explained, 

 and very little trouble is needed to imagine some process 

 by which hypothetical fundamental causes equally 

 fanciful may have led to the result which has been 

 actually observed. But when we try to prove by experi- 

 ment that this imaginary process of development is 

 indeed the true and inevitable one, much time and 



