248 



RAYMOND PEARL 



TABLE 32 



Showing the hatching records of cf 578's Fo matings 



Per cent of eggs fertile = 97.01. 



Per cent of fertile eggs hatched = 75.38. 



considered very good taking all the facts into consideration. 

 These back-cross matings of cT 578 far surpass those records. 



One can only conclude that for some reason not apparent the 

 matings 699 to 702 were physiologically extremely favorable. 

 There seems to have been a what the breeders call a 'nick' here 

 of unusual character. These matings were noticeable throughout 

 the hatching season not only for the large number of the chicks 

 produced, but also for their extra fine, vigorous character. The 

 chick mortality from these matings was low. 



As has been pointed out at the beginning of this section of the 

 paper, there undoubtedly exist differences in what might be called 

 physiological compatibility between fowls of different genotypic 

 constitutions. Some concrete data regarding this have been 

 published in a previous paper (39) . More will be presented 

 later. While some gametic combinations (at least at their first 

 synthesis) lead to physiologically weak and abnormal individuals, 

 others produce individuals which in vigor, rate of growth, etc., 

 surpass the normal. This phenomenon is perhaps more clearly 

 and strikingly shown in pre-natal mortality (embryos dead in 

 shell) than by any other character in fowls which can readily be 

 measured. I hope shortly to publish a paper on this subject, and 

 will only anticipate that paper here to the extent of saying that 

 all the experience in this laboratory with cross-bred poultry agrees 

 in showing that while there may be differences in the ease or. suc- 

 cess with which fertihzation of the egg occurs in breed crosses, 



