Adaptation to Environment 319 



that the question of use or disuse has nothing to do 

 with the production of certain harmless chemical com- 

 pounds in the body. A much more striking example 

 is offered in the case of galvanotropism. Many or- 

 ganisms show the phenomenon of galvanotropism, 

 yet, as the writer pointed out years ago, galvano- 

 tropism is purely a laboratory product and no animal 

 has ever had a chance or will ever have a chance to 

 be exposed to a constant current except in the labora- 

 tory of a scientist. This fact is as much of a puzzle 

 to the selectionist and to the Lamarckian (who would 

 be at a loss to explain how outside conditions could 

 have developed this tropism) as to the vitalist who 

 would have to admit that the genes and supergenes 

 indulge occasionally in queer freaks and lapses. The 

 only consistent attitude is that of the physicist who 

 assumes that the reactions and structures of animals 

 are consequences of the chemical and physical forces, 

 which no more serve a purpose than those forces re- 

 sponsible for the solar systems. From this viewpoint 

 it is comprehensible why utterly useless tropisms or 

 structures should occur in organisms. 



2. A famous case for the apparent adaptation of 

 animals to environment has been the blind cave ani- 

 mals. It is known that in caves blind salamanders, 

 blind fishes, and blind insects are common, while such 

 forms are comparatively rare in the open. This fact 

 has suggested the idea that the darkness of the cave 



