166 



Degeneration in the Ostrich 



TABLE VI. 



Breeders : 



South African cock, No. 140 

 North African hen, No. 11 



Chicks : 



Nine— Nos. 242, 243, 302, 



303, 305, 310 to 313 ... 



One— No. 304 



No claw 

 No claw 



No claw 

 Clawed 



genetic factors concerned are yet present in some form or other, and 

 though normally dominant, are too weak to gain somatic expression ; 

 by some fortunate gametic redistribution or somatic condition they 

 have been enabled to manifest themselves, in the one case on a single 

 toe and in the other on both. Appearing in this fashion they represent 

 " Reversions," as the term is employed by Bateson, G. B. Davenport and 

 others ; they are ancestral characters which have ceased to appear for 

 a time, and then for some reason or other make their appearance. 

 Apart from considerations of Mendelian " dominance " and " recessive- 

 ness," it is manifest that in cases where degeneration is going on genetic 

 factors may be present in the germ plasm without necessarily expressing 

 themselves in the soma; the character may or may not appear, dependent 

 upon more or less incidental circumstances. 



Where one parent is clawed and the other not, the claw generally 

 appears in about half the progeny, showing that normally the clawed 

 birds are dominant heterozygotes, which is what would be expected 

 considering the small proportion of clawed to clawless individuals among 

 the mixed assemblage of both northern and southern birds. Further, 

 where the proportions in the progeny are approximately equal, factorial 

 stability is suggested. 



TABLE VII. 



Breeders : 



North African cock, No. 78 

 South African hen, No. 225 



Chicks . 



Five— Nos. 314, 316, 320, 322, 323 

 Four— Nos. 315, 318, 319, 321 ... 



Weak claw 

 No claw 



No claw 

 Clawed 



Here of nine chicks hatched, five were unclawed and four clawed. 

 The same cock mated with a North African hen gave the like normal 

 Mendelian proportion for heterozygotes, but in two cases with a marked 

 difference in the size of the claw as between the right and left toes 

 (Table VIII). A result of this nature and other similar ones given 

 below seems to be clear proof that the genetic factors concerned with 

 the claw are by no means of fixed or constant potency, but tend to 



