384 University of California Publications in Zoology Vou. 18 
edges to the feathers. The inner portion of the barbs has no red 
in the rami, and has a series of closely-set flattened barbules, 
resembling the pennula in green speculum feathers of ducks in 
that there are constrictions between the cells, and each individual 
cell is more or less warped and spoon-shaped (Gadow, 1882, pl. 28, 
figs. 9a, b). These barbules produce a brilliant green refraction 
color, and thus give the green color to the inner portion of the 
feather. The minute details of the method of refrangent color 
production in pittas has been worked out by Gadow (1882), and 
Strong (1902). 
e) Relationships 
The Passeriformes, according to feather structure, are to be 
regarded as a compact group in which, in spite of the large number 
of species, very little divergence has taken place. It constitutes 
a terminal branch of the phylogenetic tree, its next lower relatives 
being undoubtedly the Coraciiformes, especially the suborder Pici, 
which, however, is probably to be regarded itself as a member of 
this group rather than of the Coraciiformes. 
f) Summary 
“The Passeriformes are characterized as follows: 
(1) Plumules sparse in apteria or absent entirely. 
(2) Aftershaft absent, rudimentary, or in the form of a few 
long, straggly barbs. 
(3) Distal and proximal vanules of remiges with about equal 
number of barbules. 
(4) Distal barbules of remiges very large relative to proximal 
barbules, the bases of each type about equal. 
(5) Distal barbules of inner vane of remiges with large elongate 
base, with broad filmlike subnuclear area not extending all the way 
to ventral teeth; ventral teeth small and slender, as in Coracii- 
formes, or elongate and enlarged distally; pennulum relatively 
small, the hooklets moderate and well spaced, ventral cilia short, and 
subequal, dorsal cilia small, the basal two more or less enlarged. 
(6) Distal barbules of outer vane of remiges with much shorter 
base, and relatively larger pennulum and hooklets. 
(7) Proximal barbules of inner vane of remiges with elongate, 
relatively small base, inconspicuous ventral teeth, and pennulum 
shorter than base. 
