Coukliiw] ^i [Miiy], 



opinion. Apart from his splendid observations and the great stimulus 

 to investigation which Weismann's theories have furnished, there re- 

 main many elements of permanent value in his work. 



Osborn * tliinks that "Weismann's most "permanent service to biology 

 is his demand for direct evidence of the Lamarckian principle." It 

 seems to me that his greatest service consists in the emphasis which he 

 has laid upon the intrinsic factors of development and evolution as 

 opposed to the extrinsic factors, a thing which he has indeed over- 

 emphasized, but which has sadly needed a strong defender in these later 

 years. Largely as an outcome of his work, we now recognize the pos- 

 sibilities and the limitations of the selection Iheory as never before, and 

 we also recognize that many of the evidences which were adduced in 

 support of the Lamarckian factors are not conclusive, while the method 

 of securing conclusive evidence is clearly marked out. Whatever we 

 may think of his theories, this certainly is no slight service. 



5. It is by no means an easy task to determine whether the influence 

 of extrinsic forces has really reached the germinal protoplasm and 

 modified its structure ; much more difficult is it to determine how that 

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

 the cases which are supposed to prove the inheritance of acquii-ed char- 

 acters prove only that characters are acquired, not that they ai'e inher- 

 ited. There is great need of caution against supposing that any char- 

 acter is inherited unless it repeats itself under manj^ and difiereut con- 

 ditions. Apart altogether from inheritance, similar conditions may 

 produce similar results, and consequently this source of error must be 

 eliminated if we would be certain that the structure of the germinal 

 protoplasm has really been modified. Many of the alleged cases of the 

 inheritance of mutilations, ot the direct influence of the environment 

 and of use and disuse fall away under this precaution. 



The general evidence for the inheritance of mutilations is so noto- 

 riously bad that I pass it by altogether, and select for consideration a 

 few cases, chosen from a recent work on the subject,! which have bj' 

 various writers been alleged as showing the direct influence of environ- 

 ment in modifying species and also the inherited ettects of use and 

 disuse. 



(1) 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 as showing the influence of environment in 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 A^essels. It seems very probable that 

 the diminished size of these animals is due to deficient food supply, but 

 this has so little modified the somatic protoplasm that, although thej' 

 may be fully developed as shown by sexual maturity, they at once 



* 0.sborn, Tlie Unknown Factors of Evolution, Biological Lectures, 1S9-1. 

 t K. D. Cope, The Primary Factors aj Organic Evolution, 1890. 



