56 M. R. CURTIS AND RAYMOND PEARL 



of either Li or L.. The record of 1 egg for No. 349 on January 

 26 would, on a strictly literal interpretation, put her in the 

 'under 30' class. It seems clear, however, in view of the rest of 

 her record, and of the fact, already repeatedly pointed out, that 

 March 1 does not represent biologically the absolutely invari- 

 able time of beginning of the spring cycle of production, that she 

 is really a zero winter producer. From a mating like that of 

 cf No. 627 X 9 No. 303 J one zero producer in every eight 

 offspring is expected. 



We may next consider the case of bird No. 249. This indi- 

 vidual had no full sisters. The nature of the mating from which 

 she was produced is shown by the following pedigree. 



Sire cf No. 628 X U different 9 9 

 (/L1L2 • fhl^ i 



I I 



Winter production Over 30 Under 30 Zero 



Observed 21 25 4 (+No. 249, the bird under 



discussion) 

 Expected 19.15 U.98 5.83 



In addition to the above, d^ No. 628 had four other daughters, 

 by three different females, which, because of the smallness of the. 

 families and for other reasons, cannot be exactly classified 

 genetically. These four birds were all in the 'over 30' class. 



We have classified No. 249 here as a zero winter producer 

 because all of her 9 eggs were laid between February 24 and 

 March 26. Further, all of the seven nesting records occurring 

 during the jearly spring suggests that she is the extreme of the 

 low producing segregates. It has been elsewhere pointed out 

 that March 1 does not mark biologically a fixed limit of the winter 

 cycle. Some birds, of which No. 249 is undoubtedly an example, 

 begin their spring cycle a short time before that date. 



Furthermore, the dam of No. 249, which was bird No. 436 J, 

 was of constitution fliU-Flili, with a zero winter record, and a 

 record for the year of 24 eggs. Such a bird, mated with a male 

 like No. 628, should give one in every four daughters a zero 

 producer. 



