1916] Chandler: Structure of Feathers 267 
thornlike projections, which are directed more or less distad, 1. e., 
toward the tip of the feather (see plates). Im the Falconidae they 
differ from the other dorsal cilia only in being slightly stouter and 
more thornlike (pl. 23, figs. 36a, 37a, 38a, 39a, 40a); in owls they 
are well developed but not differentiated from the other cilia (pl. 32, 
fig. 84a) ; while in a few birds, e. g. trogons (pl. 31, fig. 80a), they 
are absent entirely. On the outer vane, on the other hand, the dorsal 
cilia. of the proximal portion of the pennulum are always absent, 
at least on the first two or three cells; very frequently no dorsal 
cilia whatever are present. Usually, however, following the proximal 
two or three cells, rudimentary barbicels begin to appear, and these 
become more and more pronounced distad, the reverse condition to 
that found on the inner vane. With the exception of these few 
details, the structure of distal barbules of both inner and outer 
vanes is usually alike, and both show the same group characteristics. 
The proximal barbules (fig. E) of the two vanes are nearly always 
exactly similar in more or less of the basal portion of the barbs, but 
in the majority of birds they differ in the more distal portion of the 
barb, sometimes only at the tip, more frequently in from one-third 
to two-thirds of the terminal portion. Those of the inner vane, and 
those which are similar to them on the outer vane, have rather long 
slender bases, considerably longer than the bases of the distals, a 
series of three to six ventral teeth of differing degrees of develop- 
ment in different birds, and more or less filamentous pennula with 
only very rudimentary barbicels if any at all. With a few excep- 
tions, notably most of the ciconiiform birds, the more distal proximals 
of the outer vane differ decidedly from the others in the development 
of a series of ventral barbicels, these being formed as an increased 
number of ventral teeth, accompanied by a change in form. In 
many birds these ventral barbicels, homologous to the hooklets and 
ventral cilia of distal barbules, are very large and numerous and 
highly conspicuous, e. g., in gallinaceous and falconid birds (pl. 23, 
fig. 38c, and pl. 24, fig. 42e). Perhaps the greatest development is 
that found in Ceryle alcyon (pl. 31, fig. 79a). In many passerine 
birds, e. g., in all the Tyrranidae, the outer half of the barbs under- 
goes a very sudden and conspicuous change from plain to barbicelled 
proximal barbules (compare plate 33, fig. 92d with plate 33, fig. 93a), 
this sudden transition including a very marked reduction in the size 
of the base, and a concomitant simplification of the distal barbules, 
the hooklets of which become obsolete. This change in structure 
