J. E. DUERDEN 



173 



Since the evidence to be presented serves to establish that the scales 

 over the third toe are mostly in an incipient degenerative phase, the 

 inherent tendency may well be expected to become intensified at times 

 and to manifest itself in the chicks, though not somatically apparent in 

 either of the parents ; and it is probably as racial losses sustained de novo 

 that cases like the above, and others presented below, find their interpre- 

 tation. In general the factors concerned in the appearance of the scales 

 at the joint are so stable that no actual break in the progeny appears, 

 though there may be much variation in the degree of narrowing ; but 

 in some birds they may be in a further degenerative phase, near the 

 " breaking point," as it were, and a combination of intrinsic circumstances 

 may give an incomplete or complete break in one or more chicks, though 

 not indicated in the parents. 



Where one of the parents displays the break and not the other, then, 

 as shown below, the factor for the break acts as a simplex dominant, and 

 the interruption occurs in half the progeny. The heterozygous con- 

 dition is what would be expected considering the small proportion of 



TABLE XIY. 



Breeders : 



