48 MENDELISM AND 



treats it as a case of peculiarity in the genetics of 

 yellow pigments. On p. 102 of the same volume 

 he describes the results of crossing White Leghorn 

 with Indian Game or Brown Leghorn, the F I being 

 substantially white birds with specks of black and 

 brown, though cocks have sometimes enough red in 

 the wings to bring them into the category known 

 as pile. To test the matter I have crossed White 

 Leghorns with a pure-bred black-red Game-cock, and 

 in the offspring out of eight cocks six were fairly 

 good piles, but with not quite so much red on the 

 back as in typical birds : one was a pile with yellow 

 on the back instead of red, and one. was white with 

 irregular specks. Of the hens, four were of pile 

 coloration with breast and abdomen of uniform 

 reddish-brown colour, back, neck, and saddle 

 hackles laced with pale brown, tail white. The 

 other four were white with black and brown specks. 

 Whether these pile heterozygotes will breed true I 

 do not yet know. 



These results tend to show that factors are not 

 indivisible units, and segregation is rather the 

 difficulty of chromatin or germ plasm from different 

 races uniting together. It must be remembered 

 that the fertilised ovum which forms one individual 

 gives rise also to dozens or hundreds or thousands or 

 millions of gametes. If a given character is re- 

 presented by a portion of the chromatin in the 

 original ovum, this has to be divided so many times, 

 and each time to grow to the same condition as 

 before. How can we suppose that the divisions 

 shall be exactly equal or the growth always the 

 same ? It is inevitable that irregularities will occur, 

 and if the original chromatin produced a certain 



