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THE AMERICAN NATURALIST [Vol. LII 



appear to be without any influence whatsoever; others 

 appear to. be of varying degrees of importance. 



Thus, it is not easily possible to overemphasize the im- 

 portance of the environment in relation to egg produc- 

 tion. At best, certain elements of the environment are 

 partially controlled and similar conditions supplied to 

 the members of the flock under experimentation, but it is 

 impossible with the best practical facilities at present 

 available to furnish identical conditions to all individuals 

 of the same flock. At the very best one can only go 

 through the motions of providing such conditions. More- 

 over, one may be forced to modify the procedure selected 

 in order to keep the birds in good condition. Further- 

 more, individuals or strains may not react in the same 

 fashion to identical conditions. 



The difference in the reaction of individuals of the 

 same strain to similar conditions, particularly when these 

 conditions fall near the critical point for the strain (or 

 species), is a matter of considerable importance, espe- 

 cially when a character such as egg production is under 

 study, and more especially when it is impossible to con- 

 trol certain important elements of the environment. As 

 long as the environment is not too far from the optimum, 

 birds of low vitality, for example, may do quite as well as 

 birds of much higher vitality, but when the environment 

 approaches either end of its range, then its effects begin 

 to manifest themselves. 



A full discussion of the possible influence of the en- 

 vironment, either directly or indirectly, upon egg pro- 

 duction as a whole or upon any of the several factors in- 

 fluencing production is outside the scope of this paper. 

 While the reader should bear in mind the possibility that 

 the environment has introduced disturbing factors, every 

 effort has been made to keep all controlable elements, 

 such as feeding and housing uniform. 



Turning now to internal factors, we find that these also 

 may be considered under two heads. We have little to 

 do with the factors falling under one of these heads, for 



