No. 530] TEMPERATURE ON GROWING MICE 



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acquired characters inherited? It is my hope to convince 

 you that the method which I have employed conforms to 

 certain a priori requirements, on the one hand, and, on the 

 other hand, is workable in practise. That my results are 

 not thus far more imposing is due, I think, to no defect in 

 the method itself, but to the limitations which encompass 

 a solitary investigator, deprived of some of the generally 

 acknowledged desiderata for successful work in animal 

 breeding, such, for example, as assistants, funds and ade- 

 quate equipment. 



As to the logical requirements for such a test — to begin 

 with, what is it that we are going to test! The ' ' inherit- 

 ance of acquired characters 1 ' ? — yes and no. First of all, 

 that threadbare expression itself must be relegated to 

 limbo where it belongs. For, not only does it fail to indi- 

 cate with any precision the subject-matter of our inquiry, 

 but historically the expression has been applied to a wide 

 range of phenomena, real and alleged. Some of these we 

 now know to be fictitious; others, on the contrary, are 

 acknowledged facts; while others yet are more or less 

 debatable. It is with the debatable group, of course, that 

 we are here concerned. But, even among these, we en- 

 counter not one problem but many. Suppose, then, that 

 we drop all vague generalized expressions and consider 

 one more or less restricted problem: Are specific struc- 

 tural effects, resulting from the action of external condi- 

 tions upon organisms of one generation ever repeated in 

 the next generation under such circumstances that the 

 immediate and parallel modification of the germ-cells 

 may not be invoked as art explanation? Under "specific 

 structural effects," I do not wish to include general con- 

 ditions of health, metabolism, etc. 



What are some of the necessary conditions for a fair 

 test of this question? To begin with, we must effect our 

 modifications in the first generation. And since these 

 modifications, if repeated at all, will probably reappear 

 in a much-diminished degree, it would seem far prefer- 

 able to select characters which lend themselves readily 



