384 University of California Puhlications in Zoology f^oL. 13 



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, pi. 28, 

 figs. 9a, h). 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 Coraciif ormes, 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 booklets 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 booklets. 



(7) Proximal barbules of inner vane of remiges with elongate, 

 relatively small base, inconspicuous ventral teeth, and pennulum 

 shorter than base. 



