148 ARE THE EFFECTS OF USE INHERITED? 



potentiality of development fully equal to that 

 possessed by the long-used tibia. It lengthens 

 legs because they are used in supporting the 

 body, and shortens arms because they are used 

 in pulling. Whether it enlarges brain if used 

 in one way and diminishes it if used in another, 

 we cannot tell ; but it must obviously deaden 

 nervous sensibilities in some cases and in- 

 tensify them in others. It enlarges hands long 

 before they are used, and thickens soles long 

 before the time for walking on them. At the 

 same time, as if by an oversight, it so delays its 

 transmission of the habit of walking on these 

 thickened soles, that the gradual _and tedious ac- 

 quisition of the non-transmitted habit costs the 

 infant much time and trouble and often some pain 

 and danger. Yet where aided by natural selection, 

 as with chickens and foals, it transmits the habit 

 in wonderful perfection and at a remarkably 

 early date. It transmits new paces in horses in 



