78 GENETICS 



out of water entirely, in damp situations. These 

 land-adapted offspring, moreover, when supplied with 

 abundant water, produce in turn tadpoles which spend 

 days only, instead of months, in the water undergoing 

 their metamorphosis, thus showing an apparent inherit- 

 ance of an acquired character. 



It should be pointed out, however, that in these cases 

 the gill-breathing forms in each instance represent a 

 case of arrested development. Axolotl is simply a 

 larval form of Amblystoma which, under normal con- 

 ditions of an abundant water environment and high 

 temperature, gets no further in its metamorphosis than 

 the tadpole stage, when it produces eggs and sperms 

 and finishes its life story. A change in environment 

 simply permits the life-cycle to go on further. Chang- 

 ing from gill-breathing to lung-breathing is not, there- 

 fore, an acquired character, but a purely germinal 

 character that may be either blocked or released by 

 changing conditions in the environment. The phe- 

 nomenon is termed neotony. 



c. The Effects of Use or Disuse 



The callosities on the end of a violinist's left-hand 

 fingers are acquired by use, but they are not inherited. 

 There are callosities on the knees of the wart-hog, 

 Phacochcerus, which are also apparently the result of 

 use, for these animals kneel as they root for a living in 

 the African forests, and have done so for untold gen- 

 erations. It has been noticed that young wart-hogs 

 as soon as they are born possess the callosities, so that 



