126 ARE THE EFFECTS OF USE INHERITED? 



MARKED EFFECTS OF USE AND DISUSE ON THE 

 INDIVIDUAL. 



These are, to some extent, an argument against 

 the cumulative inheritance of such effects. When 

 a nerve atrophies from disuse, or a duct shrivels, 

 or bone is absorbed, or a muscle becomes small or 

 flabby, it proves, so far, that the average effect of 

 use through enormous ages is not transmitted. 

 When the fibula of a dog's leg thickens by 400 per 

 cent, to a size " equal to or greater than " that of 

 the removed tibia which previously did the work, 1 

 it shows that in spite of disuse for countless genera- 

 tions, the " almost filiform " bone has retained a 

 potentiality of development which is fully equal to 

 that possessed by the larger one which has been 

 constantly used. When, after being reared on the 

 ailanthus, the caterpillars of the Bombyx hesperus 



1 Variation of Animals and Plants under Domestication, ii. 

 286. 



