Inheritance of Acquired Characters 243 



if not, how can they be explained? His reply is that the 

 differences can all be accounted for on the theory of the 

 inheritance of use, for it is evident that " these gradations 

 in tactile perceptiveness correspond with the gradations in 

 the tactual exercise of the parts." Except from contact 

 with the clothing the body receives hardly any touch sen- 

 sations from outside, and this accounts for its small power 

 of discrimination. The greater sensitiveness of the chest 

 and abdomen, as compared with the back, is due to these 

 regions being more frequently touched by the hands, and 

 is also owing to inheritance from more remote ancestors, 

 in which the lower surface of the body was more likely to 

 have come in contact with foreign objects than was the back. 

 The middle of the forearm and of the thigh are also less ex- 

 posed than the knee and the hand, and have correspondingly 

 the power of tactile discrimination less well developed. 



Weber showed that the tip of the tongue is more sensitive 

 than any other part of the body, for it can distinguish be- 

 tween two points only one twenty-fourth of an inch apart. 

 Obviously, Spencer says, natural selection cannot account 

 for such extreme delicacy of touch, because, even if it were 

 useful for the tongue to distinguish objects by touch, this 

 power could never be of vital importance to the animal. It 

 cannot even be supposed that such delicacy is necessary for 

 the power of speech. 



The sensitiveness of the tongue can be accounted for, 

 however, Spencer claims, as the result of the constant use 

 of the tongue in exploring the cavity of the mouth. It is 

 continually moving about, and touching now one part, and 

 now another, of the mouth cavity. " No advantage is gained. 

 It is simply that the tongue's position renders perpetual ex- 

 ploration almost inevitable." No other explanation of the 

 facts seemed possible to Spencer. 



Two questions will at once suggest themselves. First, can 

 it be shown that the sensitiveness to touch in various parts of 



