24 



INHERITANCE OF CHARACTERISTICS IN DOMESTIC FOWL. 



are graded into the 5 classes, good (G), fair (F), poor (P), nonnal though 

 of abnormal ancestry (N), and normal of normal ancestry (N'),it follows: 

 "first, that the proportion of polydactylous young produced by a male 

 decreases in the successive classes from G to N'; and, secondly, that the 

 degree of development of the toes produced on those polydactylous young 

 diminishes in the same order." It is possible to test this conclusion in 

 poultry because, inside of any one type of extra-toe, e. g., the triplex type, 

 variation appears in the absolute size of the toes and in the degree of their 

 separateness. Our questions, then, are: (1) does the proportion of poly- 

 dactyl young produced by a pair of birds of any type diminish with the 

 degree of development of toes inside of that type, and (2) does the degree 

 of development of the toes produced on the polydactylous offspring diminish 

 in the same order? 



Table 16. — Distribution of toe-numbers in the offspring of 4^toed heterozygotes. 



Table 17. — Distribution of toe-numbers in the offspring of extracted 4-toed parents. 



Two sets of data are available for answering these questions. The most 

 direct set includes the data derived from crossing "pure-bred" polydactyl 

 birds and the other includes the data derived from using hybrids between 

 normal-toed and polydactyl ancestors. The latter data have the advantage 

 that the parents offer a greater variability; but they have the disadvantage 

 that the germinal condition of those parents is incompletely known. 



The pure races may be considered first. Eight matings of Houdans, 

 each parent with 5 toes, gave 122 offspring, of which 116 had 5-5 toes, 

 3 had 4-5 toes, and 3 had 4-4 toes. The variability of the toes is not great 

 in the parent Houdans. But, arranging them in the order of development 

 of the toes, the most developed first, the series of table 18 results. 



