68 INHERITANCE OF CHARACTERISTICS IN DOMESTIC FOWL. 



The area of the head occupied by the crest is also variable. This was 

 estimated in tenths for each of the parents and offspring. Two principal 

 centers of variation appeared, at 3 and at 8, or roughly one-third and two- 

 thirds the full area. The results, being based on estimates, are not wholly 

 satisfactory, but so far as they go they indicate that when both parents 

 have a crest that belongs to the lower center of variation their offspring 

 belong chiefly if not exclusively to that center ; but when they both belong 

 to the upper center of variation a minority of the offspring belong to the 

 lower center. Provisionally it may be concluded that extensive crest is 

 dominant over the restricted crest or that there is an "extension factor." 



