SUMMARY AND CONCLUSION. 23 



result that falls into the same category as the "reversion" of the 

 goldfinch hybrid. In all cases the hybrids with the yellow canary 

 are very variable and frequently show more or less of the canary yel- 

 low. This is due to the mottling factor of the canary to which refer- 

 ence has been so often made. That it is the yellow canary which 

 contains the mottling factor and is the source of the variability of the 

 hybrids is shown by the facts that (1) hybrids with the green canary 

 do not vary in this fashion, and (2) hybrids between any two species of 

 finches — of which many are bred by fanciers — are "cast in one mold." 



D. SUMMARY AND CONCLUSION. 



The history of the domestic canary shows that it has been intensely 

 bred for only about 250 years and may therefore be regarded as a rela- 

 tively recently acclimated species when compared with poultry that have 

 been bred for over 2,000 years. Nevertheless distinctive characters have 

 arisen which behave in Mendelian fashion. 



Crest is dominant over plain head. 



Baldness is a unit-character and is recessive to perfect crest. 



The yellow canary is derived from the original "green" canary 

 by the loss of black. It carries a mottling factor. Consequently when 

 the yellow canary is crossed with a pigmented canary or with a finch 

 the hybrids are mottled. 



The mottling is not a fixed pattern. The spots vary in position 

 and relative size — they may cover nearly the whole body or they may 

 form a mere "ticking." The degree of mottling is inheritable. Ticking 

 behaves as a unit-character. 



Mottling is a heterozygous character and throws mottled, clear 

 yellow and self-greens. 



The principle of localization of the units of a complex plumage 

 must be recognized. The cap of the Lizard canary, the red face of 

 the goldfinch, the shoulder striping of the green canary are not only 

 unit-characters but they occur only at their proper localities and in 

 their proper forms in the body plumage. In mottled canaries the 

 presence of black on the shoulder means striping, on the wing it means 

 dead black, white-laced remiges, on the mid-breast it means a uniform 

 olive color. The plumage of a yellow canary may be compared with a 

 letter that has been written with invisible ink. Wherever the developer 

 acts (i. e., the black pigment of the green canary is added) that which 

 is written appears with all of its idiosyncrasies. 



Cold Spring Harbor, N. Y., 

 September 28, 1907. 



