SOME RESULTS OF OSTRICH INVESTIGATIONS. 279 



birds a single break occurred in three cases and a double break 

 in two. They represent a definite loss of toe scales, and, taken 

 along with the other facts of degeneration in the foot, are 

 without doubt to be regarded as the first evidence of degeneration 

 in the nu'ddle toe of the ostrich, the first, second, and fifth having 

 already disappeared, and the small, fourth, being well on the way. 

 The breaks evidently represent independent unit characters, 

 retrogressive mutations, in course of introduction within the 

 whole race, the process having gone a little further in the 

 northern ostrich than in the southern. 



Breeding experiments prove that the breaks are germinal 

 in their nature. Where no break occurs in either of the parents 

 the progeny also show none. Thus in 13 cross-bred chicks from 

 a southern cock and a northern hen, both with a continuous 

 scutellation, no loss of scales occurred. When, however, one of 

 the parents bears a break and not the other, then, as indicated 

 below, approximately one-half of the chicks displays it, proving 

 that the factor for the break is dominant, but that the germ 

 plasm is simplex or heterozygous with reference to it. 



Tarle 10. — Scutellation in Parents and Chicks. 



Break. 



X 



X 



X 

 X 



X 



X 



The heterozygous condition as regards the break is what 

 would be expected, assuming that the character is one which is 

 in process of introduction within the race, and that it behaves 

 in Mendelian fashion. At present the mutation is found in com- 

 paratively few individuals, and in a state of nature there is little 

 chance that a bird showing the break would mate with another 

 in a like condition, but rather with one having the scales con- 

 tituious. If the genetic change first took place in a homozygous 

 duplex form in a few individuals, there is small likelihood that 

 these would mate with others in like condition, but with nullifiex 

 individuals. The first crosses would be dominant and simplex, 

 and these, mating with other nullifiex birds, would give half 



