1921.] 



Research in Animai. Breeding. 



331 



work necessary to complete it. \Var difficulties, however, forced 

 us eventually to abandon the work before it was finished, and 

 since the x\rmistice the funds available for this kind of research 

 have not been sufficient to justify us in undertaking fresh experi- 

 ments on these lines. Such results as we managed to obtain 

 are not without interest, especially in view of the economic 

 importance of the characters investigated. We began in the 

 usual way, crossing birds of a brown-egg broody strain with birds 

 of a white-eQ;f^ non-broodv strain. For the former we selected 

 the Black Langshan, and for the latter the Brown Leghorn and 

 the Gold Pencilled Hamburgh. In respect of egg-colour the first- 

 cross hens were intermediate, though the tinted eggs they laid 

 approximated more to the lighter than the darker kind of the 

 parental breeds. In the F2 generation nearly 120 birds were 

 tested, and great variation w^as found. Some laid white eggs, 

 a few laid dark eggs resembling those of the Langshan. w^hile the 

 great majority laid tinted eggs. The grades of tint varied from 

 nearly w^hite up to full brown. For a given hen the grade was 

 fairly constant, though it varied somewhat with the season, 

 especially in the case of those birds laying the more deeply 

 tinted eggs. 



In its broad outlines the case was not unlike the weight case 

 in poultry; viz., an intermediate Fl generation of fair uni- 

 formity, and an F2 generation showing a full range of variation, 

 betw^een and including the two parental forms (Fig. 6, p. 254). It 

 is probable that here also we are dealing with several factors, 

 each of which influences the tint of the egg ; and 0¥ir experiments 

 have shown further that such factors are transmitted by the 

 cock as well as by the hen. There is evidence also of the exist- 

 ence of a factor which inhibits pigmentation of the shell, and 

 this factor would appear to be linked with the factor for black 

 down. Fl birds from the Langshan and Brown Leghorn cross 

 all have the dominant black down of the Langshan. In F2 the 

 brown-striped down of the Leghorn reappears in a quarter of 

 the chicks. Our testing results showed that the layers of white 

 and nearly white eggs were relatively much more numerous 

 among the pullets that hatch black in down than among those 

 that hatched brown. This peculiar linking of characters, though 

 familiar to plant breeders, has not often been met with among 

 tho higher animals. Probably this is because relatively little 

 work has yet been done with birds and mammals. It is likely 

 that, as our knowledge increases, these cases of linkage between 

 ■characters will become more plentiful and it is not improbable 



