THE FACTORS OF ORGANIC EVOLUTION. m 



modification takes place. I believe it is safe to say that 

 a majority of the cases which are supposed to prove the 

 inheritance of acquired characters prove only that char- 

 acters are acquired, not that they are 

 Do external inherited. There is great need of cau- 



. , tion agamst supposing that any charac- 



germinal ..,.',. 



protoplasm? ^^^ ^^ mhented unless it repeats itself 



under many and different conditions. 

 Apart altogether from inheritance, similar conditions 

 may produce similar results, and consequently this 

 source of error must be eliminated if we would be cer- 

 tain that the structure of the germinal protoplasm has 

 really been modified. Many of the alleged cases of the 

 inheritance of mutilations, of the direct influence of the 

 environment, and of use and disuse, fall away under this 

 precaution. 



The general evidence for the inheritance of mutila- 

 tions is so notoriously bad that I pass it by altogether 

 and select for consideration a few cases, chosen from a 

 recent work on the subject,* which have by various 

 writers been alleged as showing the direct influence of 

 environment in modifying species and also the inherited 

 effects of use and disuse. 



[a) It is well known that certain gasteropods if 

 reared in small vessels are smaller than when grown in 



large ones, and this case has been cited 



Diminished u • ^.u • a r • 



as showing the influence of environment 



nutrition. . ,., • • rr^i 



m modifying species. There is good 



evidence, however, that this modification does not affect 



the germinal protoplasm, for these same gasteropods 



will grow larger if placed in larger vessels. It seems 



very probable that the diminished size of these animals 



is due to deficient food supply, but this has so little 



* E. D. Cope. The Primary Factors of Organic Evolution, 

 1896. 



