1896.] METALLIC COLOURS OF BIRDS. 289 
well-developed lamina; therefore in this case metallic barbules can 
occur only towards the middle of the barb in contour-feathers, for 
this is the only place where the lamina is well-developed. In 
other words, in contour-feathers the metallic band cannot be, or is 
not primitively, terminal. Where it seems to be terminal, as in 
the feather described above, this is accomplished by a total or partial 
suppression of the terminal barbules, the naked barb persisting 
and forming the delicate fringe already noticed. This does not, 
however, occur in quill-feathers to the same extent, because these as 
a rule are characterized throughout by having barbules with very 
well-developed lamine. Thus it is by no means uncommon to 
find terminal bands of metallic colour in the tail-quills of Humming- 
birds, or we may find the whole surface metallic : there never seems 
to be a longitudinal edging of metallic colour. 
Conviction as to the truth of the statement here made, that 
metallic bands on the contour-feathers of Humming-birds are not 
primitively terminal, is best attained by considering a series of 
cases. 
In Eustephanus galeritus, female, the breast is covered with greyish 
feathers which have near their centre a spot of brownish pigment 
which shows a faint metallic-green sheen. In the breast-teathers 
of E. fernandensis, female, undoubtedly a more specialized species, 
the spots are not much larger but the pigmentation is darker, and the 
metallic colour is much more brilliant. This kind of metallic colour- 
ing is very frequent, especially among the females of many species or 
genera (cf. the species of the genus Oreotrochilus). If the barb of 
such a feather is examined microscopically, it is seen that all the bar- 
bules with well-developed lamin contain pigment and are metallic. 
Towards the base of the barb the barbules are colourless and downy, 
towards its apex they are colourless and short, the lamina is rudi- 
mentary, the filamentous portion is somewhat expanded and bears 
only rudimentary cilia (Pl. XI. fig. 11). Between this type and 
that of the gorget-feathers of Basilinna Icucotis (Pl. XI. fig. 12) 
there are all stages in the suppression of these apical barbules. Thus 
in Eustephanus fernandensis, female, itself the feathers of the poste- 
rior region of the back are brilliant green, but are quite distinctly 
tipped with white. In the specialized crest which this female is 
almost peculiar in possessing this white edging is much reduced, 
but the colourless apical barbules are still quite visible with a lens. 
In general, we may say that while the feathers of the specially 
brilliant patches have barbs with naked tips, the ordinary metallic 
contour-features have barbs which bear at their tips a series of 
non-metallic barbules. Thus the green feathers on the back even 
of Basilinna leucotis have a distinct border of pale rufous colour. 
This is of some interest from the point of view of the development 
of the metallic colours of Humming-birds. In Phaethornis eurynome, 
one of the so-called ‘hermit’ forms without any brilliancy of 
colour, the feathers of the back are greyish black edged with a 
broad band of yellowish colour; the dark region exhibits a very 
faint greenish sheen. If we begin with a type like this, the evolu- 
Proc. Zoo, Soc.—1896, No. XIX. 19 
