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THE AMERICAN NATURALIST [Vol. LIV 



of friction and pressure. On this interpretation a new 

 character, to wit, a callosity, can arise either before or 

 after hatching as a result of the responsive nature of the 

 tissues, apart from any germinal representation. 



Acquired adaptive characters, structural responses to 

 internal or external stimuli, are by their very nature 

 extra-germinal, and their appearance may well lead us to 

 hesitate in accepting the germ plasm theory as a complete 

 interpretation of everything somatic, or of everything 

 that is transmitted from generation to generation, des- 

 pite the statement by Dr. C. B. Davenport 11 that: "Upon 

 one point all geneticists are, however, agreed . . . that 

 we must interpret all our results in terms of genes alone. ' ' 



So plastic and so responsive -are the parts of the or- 

 ganism to stimuli that, in spite of such an embracive pro- 

 nouncement, it may still constitute a subject for enquiry 

 whether many of the adaptive relationships in organisms 

 are not such as were originally impressed upon the indi- 

 vidual as a result of its activities or subjection to former 

 stimuli and which have in time become transmissible. 

 The problem has been neglected for the past two or three 

 decades as a result of the firm hold which the germ plasm 

 theory of inheritance has gained over the minds of biol- 

 ogists and the general acceptance of the non-heritability 

 of acquired characters. Renewed search will probably 

 disclose many other instances of characters appearing 

 pre-natally which 'could just as well be developed as 

 needed in the life-time of the individual, and thereby 

 throw suspicion upon their germinal origin. Callosities 

 are undoubtedly the most direct and simple instances of 

 this nature which could be adduced ; we have both trans- 

 could have been formed post-natally just as readily as 

 those produced where pressure and friction are applied 

 to surfaces not already callous. Knowing also the re- 



