Brewster on a Collection of Arizo??a Birds. 1 35 
The brilliant colors of these feathers have often been ascribed 
to irregularities of surface, the traces of the cell cavities being 
mistaken for pits on the surface That this is an error is at once 
shown by examining a section. 
Before leaving the subject I cannot refrain from calling atten- 
tion to the wonderful diversity of means employed, as well as 
their complexity in the production of feather colors. Among 
the Parrots we have the most skilful painting combined with ac- 
cidental colors. Yet all ornithologists base specific differences 
on slight variations of color, and this in spite of the fact that 
birds may change their color according as they are wet or dry, 
owing to the nature of their food, or to slight differences in the 
quantity of pigment. 
In this they are no doubt often right, but when we come to 
varieties based on the very faintest distinctions of color and form, 
we may well pause till more is known of avian physiology. 
EXPLANATION OF PLATE I. 
Fig. i. Diagramatic representation of the effect of a film on light. 
Fig. 2. Transverse section of a barb of Chloropkanus atrocristatus; 
Hartnack 3-9 im. the light part yellow, the dark part dark brown. 
Fig. 3. Transverse section of a barb of Cyanocitta cristata. Hart. 
3-9 im - 
Fig. 4. Same of Cyanospiza cyanea $ . 
Fig. 5. Two sections of a barbule of a Peacock. 
Fig. 6. Section of barb of Sicilia sialis much magnified. 
ON A COLLECTION OF BIRDS LATELY MADE 
BY MR. F. STEPHENS IN ARIZONA. 
BY WILLIAM BREWSTER. 
( Continued, from p. 94.) 
33. Feucedramus olivaceus ( Giraud ) Coues. Olive- 
headed Warbler. — The Olive-headed Warbler, one of 
Giraud’s famous “sixteen” Texas species, has found an unques- 
tioned place in our fauna only on the strength of three Arizona 
specimens, taken by Mr. Henshaw at Mount Graham, in Septem- 
