GENERAL TOPICS IN INHERITANCE. 



8 9 



development in alba of the striping determinant is accounted for. When the 

 sperm of gilva, bringing the active principle for striping, fertilizes the egg 

 of alba with its striping determinant, the striping makes its full appearance. 

 These two or three examples from both plant and animals indicate a method 

 of explaining hybrid forms that is probably of wide applicability. 



Are the hybrid forms of poultry to be explained on the atavistic or the 

 rtictilate inheritance theory? Take first the case of barring. Three 

 tests can be applied : First, inherent probability from the ancestry of the fowl 

 crossed ; second, general distribution of barring among the offspring ; third, 

 proportion of different forms of plumage pattern in generations beyond the 

 first. The cross between Tosa fowl and White Cochin gave barred birds. 

 If the barring were latent it must have lain in the Cochins the form without 

 visible pattern. It is fairly certain that neither of the ancestors of domestic 

 fowl was barred ; hence if the barring determinant existed in the Cochin 

 bantam it must have been introduced by a recent cross. Bantamizing of 

 Cochins is effected by crossing with some bantam race, .but until recently 

 no barred bantams have been created. It is therefore highly improbable 

 that a barred bird was used to bantamize the Cochins. While it is possible, 

 it is improbable that the White Cochin contained a barred determinant. 

 Second, barred races have the two sexes equally barred, but our hybrids 

 are barred in the male only ; consequently barring here acts like a neomorph. 

 Third, on the theory of atavism we should expect to get in the second hybrid 

 generation : 



The actual proportions of the three types accord much better with the 



f 'particulate inheritance theory than with that of atavism, but the total number 



of offspring is insufficient to give certainty. It may be concluded that while 



the evidence does not exclude the atavism theory of the cropping out of 



barring, it favors the theory of particulate inheritance. 



The case of the hybrid between single and V comb rests on more extensive 

 data. These are set forth on pages 10-12, and are less favorable to the ata- 

 vistic theory than to the particulate theory. 



The other heterozygous forms have been less carefully studied. They are 

 the blue, Andalusian (fig. 54, pi. xvii), plumage color resulting from a 

 white and a black crossed, and the case of the down of the hybrid Minorca X 

 Dark Brahma chicks. This is black like the Minorca, but lacks the white 

 of the chicks both of that race and of the Dark Brahma. The Andalusian 



