ACQUIRED CHARACTERS 79 



this instance looks like one of inheritance of a charac- 

 ter acquired through use or exercise. 



The skin on the soles of human feet is thicker than 

 the skin elsewhere, and by use it becomes still thicker. 

 This is apparently another instance of the same sort. 

 The writer has observed, however, that a cross sec- 

 tion through the foot of a "mud puppy," Necturus 

 maculatus, shows a much thickened sole. Necturus, 

 it should be noted, is a very primitive salamander 

 living always under water and never using the soles 

 of its feet in any way to bear its weight, nor is it 

 reasonable to suppose that it ever had any ancestors 

 who did so, for the hands and feet of the Amphibia 

 are the most primitive and ancient hands and feet to 

 be found in the animal kingdom without any known 

 ancestral types. The thickening of the skin on the 

 sole of the mud puppy's feet must be due, therefore, 

 to germinal determiners and is in no way an acqui- 

 sition through use. The same may also be true of the 

 wart-hog's knees and of human soles. 



The strong arm, the skilled hand, and the trained 

 ear are not inherited. They have always to be re- 

 acquired in each succeeding generation just as surely 

 as the ability to walk, or to read and write. 



Herbert Spencer has defined instinct as "inherited 

 habit." But surely those instincts which determine a 

 single isolated action during the lifetime of the indi- 

 vidual, such as the spinning of a peculiar cocoon, can- 

 not be the result of habit, since habits are formed only 

 through repeated action. 



Dr. Hodge, who succeeded in hatching tame quail 



