254 University of California Publications in Zoology  {Vou. 138 
VENTRAL TEETH (figs. D and E). Anteriorly projecting, ventral, basilar bar- 
bicels of both distal and proximal barbules of nearly all birds, often 
lobate or leaflike in distal barbules, usually toothlike in proximal bar- 
bules. Synonym: toothlike processes (Wray, 1887); ventral lobes 
(Mascha, 1905). German synonym: ventrale Lappen (Mascha, 1904). 
FLEXULES (pl. 17, fig. 10e). A new term used to designate the curved bar- 
bicels occurring on the dorsal edge of the bases of distal and proximal 
barbules of the trunk feathers in some groups of birds (see p. 272). 
Hitherto apparently unknown. 
Nopes (fig. F). The junction of the cells of the pennulum of down bar- 
bules, usually characterized by swellings or outgrowths of some sort. 
Prones (fig. F). Short, spiny outgrowths at the nodes of the down of 
many birds, differing from other barbicels in that three or more may 
occur on the distal end of a single cell, whereas there are never more 
than two cilia or other kinds of barbicels on a single cell. 
V. MeruHops 
After experimenting with various methods of preparing feathers 
for microscopic study, especially the barbules, it was found that in 
most cases the examination of dry mounts of barbs and barbules 
gave entirely satisfactory results. This was at the same time so 
simple, and took so little time in preparation, that it was possible 
to examine the microscopic structures of the feathers of a very large 
series of birds, and thereby to determine with considerable precision 
the constancy and uniformity of characters in various groups. 
The barbs were first studied under the microscope with their 
vanules intact. The vanules were then spread backward in order 
to separate the barbules for individual study, this bemg done by 
merely drawing the barb, tip first, between the thumb and forefinger. 
With a scalpel some of the barbules from each vanule were scraped 
off from the region of the barbule which it was desired to study, 
and mounted dry under a cover glass. In this way a considerable 
number of individual barbules could be separated, and as they would 
lie in all sorts of positions, their general form could be studied 
readily from such a preparation. The morphology of heavily pig- 
mented structures could be studied more easily when mounted in 
balsam. In some eases also barbules were mounted in balsam in 
order to determine whether certain appearances were due merely 
to pigmentation, or to structural modification, and to determine 
the effect of oils of low refractive index on color-producing mechan- 
isms. The methods of treating individual birds and groups of birds 
to determine their epiphyologic characters will be discussed at the 
beginning of Part II. 
