Appendixes 319 



Appendix to Chapter X. 



With respect to sex-limitation a great deal of recent 

 evidence has been discovered. Several characters in Poultry 

 have been shown to follow the same system of descent as 

 the black colour of Canaries. Especially may be mentioned 

 the barred markings of Plymouth Rock (Pearl and Surface, 

 Arch. Entwm. xxx. 1910). This barring is a dominant, 

 males being homozygous and females heterozygous. The 

 females crossed with black males give black females and 

 barred males. 



Staples-Browne (Jour. Gen., 1912, n. p. 158) gives 

 additional evidence that the brown colour of the Barbary 

 Dove is similarly sex-limited, crosses with a white male 

 giving usually dark males and white females. 



Gerould (Amer. Nat., 1911, p. 257) has investigated 

 the case of the white females of Colias, showing that white 

 is probably dominant in the female, recessive in the male ; 

 and much work has been done in reference to the poly- 

 morphic females of tropical butterflies, several of which 

 have been shown with great probability to follow a simple 

 Mendelian scheme in their descent (see especially Punnett, 

 Mendelism, ed. 3, 1911, p. 134; Spolia Zeylanica, 1910, 

 vii. in which the case of Papilio polytes, aristolochiae, and 

 hector is elucidated). 



The subject upon which the most extensive work has 

 been done is Drosophila ampelophila, the pomace-fly, 

 especially by T. H. Morgan (chief paper in Jour. Exp. 

 Morph., 1911, vol. xi). The eyes are of several colours, 

 dark red, vermilion, orange, white, &c., and complex rules 

 of sex-limitation have been found governing their descent. 

 The simplest case is that of red eye and white eye, which 

 follow the same rules as colour-blindness in man, white eye 

 being the equivalent of colour-blindness. The whole subject 

 is full of interest, but could only be made clear at great 

 length. 



In regard to colour-blindness and analogous phenomena 

 Doncaster has made a suggestion of great importance (Jour. 

 Gen., 1911, i. p. 377). Hitherto we have supposed, following 

 the analogy of horns in sheep, that the colour-blindness 

 must be the dominant, for the reason that the normal male 



