THE AMERICAN NATURALIST [Vol. LII 



others, such as rhythm, are almost inseparable from egg 

 production itself. The numerical record of a hen shows 

 only the number of eggs laid, but does not show the com- 

 ponent elements which enter into the making of such a 

 record. All these various elements must be studied in- 

 dividually and the influence exerted by each on egg pro- 

 duction worked out. Moreover, the mode of inheritance 

 of the separate factors must also be determined. 



Further, it should be noted that the interrelation of 

 the various factors is so complex that it is difficult to 

 describe each by itself. In nearly all cases the bearing 

 of some other factors must be considered to a certain ex- 

 tent, at least, along with that factor which is specifically 

 under discussion. 



It is important to observe that while the results ob- 

 tained for the Rhode Island Reds described in this paper 

 differ in several respects from those obtained by Pearl 

 ('12) for Barred Plymouth Rocks, these differences are 

 inherent in the birds themselves and are on a par with 

 the visible differences, such as color, that exist between 

 the two breeds. Pearl has anticipated that differences in 

 fecundity in various strains and breeds are likely to be 

 found. He states as follows: 



The writer has no desire to generalize more widely from the facts set 

 forth in this paper than the actual material experimentally studied 

 warrants. It must be recognized as possible, if not indeed probable, 

 that other races or breeds of poultry than those used in the present ex- 

 periments may show a somewhat different scheme of inheritance of 

 fecundity. ... I wish only to emphasize that nothing is further from 

 my desire or intention than to assert before such investigations have 

 been made that the results of the present study apply unmodified to all 

 races of domestic poultry. 



It is clear, then, that a complete knowledge of fecundity 

 and its inheritance in domestic birds can only be ob- 

 tained by a careful study of egg production in all breeds 

 and perhaps even in several strains of the same breed. 

 As shown later on, one of the several factors that deter- 

 mine winter egg production is characteristic of Pearl's 



