378 University of California Publications in Zoology Vor. 13 
colors which are due entirely to refraction, the pigment being of a 
totally different color. It is interesting to note that in blue 
iridescent feathers the underlying pigment is a rich rufous brown, 
in green a duller fuscous brown, and in all shades of red a very 
dark olive-green, brighter in the fiery red of Selasphorus rufus 
than in the lilac or ruby red of other species. This phenomenon 
is explained by the theory of selective transmission and reflection, 
colors which are readily reflected being poorly transmitted. 
In various other types of coraciiform birds still other interesting 
color modifications are to be found, only a few of which may be 
mentioned here. The coppery green of Jacamerops grandis is pro- 
duced by barbules very similar in form to those of hummingbirds, 
the color being reflected from the portion of the barbule not curved 
over, as in Petasophora. Green in the Capitonidae is produced in 
an interesting manner, the portion of the ramus ventral to the 
attachment of the barbules having a deep yellow pigment color, 
while dorsal to the barbules the rami are curved over flangelike, 
contain a rich brown pigment, and produce a blue structural color. 
The combination of blue and yellow by reflected light gives the 
effect of green, while by transmitted light it is orange brown. The 
depth and tone of the color varies with the pigment in the non- 
refrangent barbules. In the woodpeckers the red crests which are 
so frequently found owe their color to prolonged, cylindrical rami 
which are filled with a deep red pigment. The peculiar effect of 
the white and red streaked breast of Asyndesmus torquatus is due 
to a deep red pigmentation in the dorsal half of the rami, and a 
white effect in the ventral half, appearing under the microscope 
like a miniature snow bank, due to the countless minute air spaces 
which cause diffusion of light. 
e) Relationships 
The Coraciiformes, as stated at the beginning of the discussion 
of them, constitute a rather heterogeneous assemblage of birds which 
lie between the Cuculiformes and the lower orders on the one hand, 
and the Passeriformes on the other. The Coraciidae and near 
allies, Striges, Caprimulgi, Bucerotidae and Cypselidae, have types 
of feathers which are to be regarded as independent offshoots from 
the main line of evolution. The trogons seem to be more nearly in 
the line of descent of the passerine birds, the Rhamphastidae and 
Capitonidae of the suborder Pici connecting them with the latter 
