INHERITANCE OF FECUNDITY 233 



earlier in this paper one cannot expect to get a normal somatic 

 expression of the hereditary constitution in respect to fecundity 

 unless the bird is a physiologically normal, well-developed individ- 

 ual. Stunted, under-developed, or physiologically unsound birds 

 will lay but very few if any eggs, regardless of what fecundity 

 factors it may carry, A marked difference is here apparent be- 

 tween structural and physiological characters so far as the study 

 of inheritance is concerned. A definite structure either is or is 

 not present in the zygote, however weak physiologically the indi- 

 vidual may be. But if the general capability of an organism with 

 respect to the transformation of matter and energy is markedly 

 reduced, then all physiological characters will be affected, and fail 

 to reach complete normal expression. 



In the study of cross-bred poultry I have found pure extracted 

 whites from crosses involving originally two heavily pigmented 

 parent races to be conspicuously good examples of the phenome- 

 non under discussion. It is only very exceptionally, in my 

 experience, that such white birds are physiologically normal. 

 Indeed because of this fact it is only with the greatest difficulty, 

 and after many failures, that I have been able to get such extracted 

 whites to breed, and thus form a pure white race. If the hens 

 lay eggs, which some do not do, they are usually either infertile, 

 or else all the embryos die at an early stage. These facts have 

 some bearing on the popular belief of animal breeders that whites 

 in general are delicate in constitution and hard to rear. This 

 belief is so well known that it is not necessary to cite in detail 

 references regarding it in the literature. 



As a consequence of the above considerations, I have felt 

 justified in leaving out of account, or rather in considering apart 

 from the others, a few of the Fo individuals, in all some 7 out of 

 over 200 Fo birds all told. In each case these birds were physio- 

 logically abnormal, and obviously so to the most casual observer. 

 The fact that they did not lay was no criterion whatsoever of 

 their hereditary constitution. In order that there might be no 

 possibility of unfairly influencing ratios by leaving these birds 

 out, the whole families (usually of two or three individuals only) 

 to which they belonged have been rejected. As a matter of fact 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 13, NO. 2 



