1911] Griimcll: The Linnet of the Heiwaiian Islands. 191 



are colored) of males after the post-juvenal molt, is red. There 

 occur rather infrequently, irrespective . of locality, individuals 

 of three other color categories: yellow (most rarely), orange, 

 and red with yellow or orange feathers intermixed. 



A series of male linnets collected in the Hawaiian Islands in 

 1910 are all of the yellow or orange type of coloration. The lin- 

 net of the Hawaiian Islands is known to be of exotic origin. It 

 is believed to have been introduced less than forty years ago, 

 the imported individuals having been obtained in the vicinity of 

 San Francisco, California, where the common red type is known 

 to have prevailed ever since birds have been observed in the 

 region, a period of sixty years at least. 



The peculiarities of the Hawaiian linnet are similar to those 

 presented in rare cases, sporadically, by the linnet of the main- 

 land of North America and by individuals kept in confinement. 



The foregoing consideration of the various factors which may 

 have had to do with the acquiring by the Hawaiian linnet of 

 the yellow or orange type of coloration exclusively, leads to the 

 following conclusions : Their peculiarities as now presented are 

 nejt to be considered manifestations of ordinary individual varia- 

 tion, not seasonal, and not the result of individual senility. 

 Going back to the primary actuating causes they must be at root 

 due in some way to change in habitat. 



The physiological machinery by which these causes have 

 brought about the ultimate results is doubtless extremely intri- 

 cate, though portions of the process are becoming understood. 

 The causes themselves may lie among a multitude of elements 

 constituting the environmental complex. 



Evidence is presented in this paper which would appear to 

 eliminate the action of several of the more obvious environ- 

 mental factors (temperature, humidity, change of food, reduc- 

 tion of enemies). One apparent circumstance would appear 

 significant, however, namely, that the off-color character is asso- 

 ciated with insularity of habitat. A deficiency in capacity, of 

 the germ, for the formation of the appropriate enzyme may have 

 been intensified through close breeding until the condition was 

 reached where the amount of enzyme produced in the feather 



