No. 573] 



551 



produced, must have been superabundant. Ward (1908) 

 has described a case of a black robin becoming albinistic 

 and reviews a number of such cases. The ability of the 

 same feather follicles in different moults to produce 

 feathers with different sorts or amounts of pigment is 

 thus evidenced and has lately been carefully studied by 

 Pearl and Boring (1914) in the hen. 



In addition to the case of the robin above mentioned, 

 the white line marking off the crown patch from the ear 

 patches is sometimes found abnormally in other birds. 

 Thus Sweet (1907) records two slate-colored juncos 

 (J unco liifcnialis) taken in March, 1903, at Avon, Maine, 

 in which there was a white line above the eye, and the 

 black throat patch was absent, owing no doubt to the 

 ventral restriction of the neck patches, as often seen, for 

 example in pigeons. Maynard 1 figures the head of a 

 young female black-poll warbler (Dendroica striata) in 

 autumn, showing an inclination to assume a white super- 

 ciliary stripe. I am convinced that this mark so common 

 in many birds, is merely a development of the primary 

 break marking off the crown patch from the ear patches 

 so that it has become a permanent part of the pattern. 



The failure of the crown patch to develop at all, as is 

 sometimes the case in the domestic pigeon, results in a 

 white-crowned bird. In the West Indian Columba leuco- 

 cephala, exactly this modification lias taken place and the 

 entire top of the head is permanently white. The same 

 condition is found in sundry other genera, including a 

 humming bird, a heron, and others. It would be inter- 

 esting to discover by experiment if it were not easier to 

 produce a definite white marking through selecting for 

 the non-development of a certain patch or patches, than 

 to try to restrict a certain pigment patch to definite 

 bounds as in the experiments of Dr. MacCurdy and Pro- 

 fessor Castle (1907). 



The crown patch as a separate unit in pigmentation, is 

 often of a different hue from the surrounding patches. 



i "Birds of E. North America," 1896, p. 585. 



