288 MISS NEWBIGIN ON THE [Feb. 18, 
colour, it may be noticed as a fact for future investigators that, as 
is indicated in the figures, the lamine in the feather described show 
more or less distinctly an arrangement of cross-bars (or compart- 
ments). This is common in the case of the Humming-birds, but it 
is also sometimes distinctly visible in the laminz of the barbules of 
Sun-birds (see Pl. XI. fig. 3 and Pl. XII. fig. 18), so that its signi- 
ficance is somewhat doubtful. One other fact in connection with 
the metallic colour may be noted. Contrary to the usual rule, the 
feather of the Humming-bird mentioned under certain circumstances 
exhibits metallic tints by transmitted light even under 3” objective. 
When this occurs, it is clearly seen that the colour is confined to the 
dark infolded part of the barbule, which alone under ordinary cireum- 
stances is visible (see Pl. XI. fig. 10). This irfolded part cannot, 
however, be itself the cause of the metallic colour, for it is absent 
from the metallic feathers in some cases (see Pl]. XII. fig. 19). 
The ridging of the surface of the feather produced by the way 
in which the barbules are inserted, though apparently a factor in 
colour production, cannot be absolutely essential, for it is some- 
times absent. Thus, in Calothorax lucifer in the brilliant throat- 
patch the feathers in the middle line are very distinctly ridged and 
have the usual plate-like structure, while those at the sides of the 
throat are quite devoid of ridges but do not show diminished 
brightness. Similarly, in Cyanolesbia gorgo the brilliant green 
feathers of the crest are perfectly smooth, and have a certain hard 
gloss which is absent in the ridged feathers. 
The fact that in Humming-birds it is the proximal, and in Sun- 
birds the distal region of the barbules which is metallic has more 
effect upon the general coloration than might at first sight be 
supposed. It is, in the first place, now obvious that there is no- 
thing in the structure of the metallic feathers of Humming-birds 
which is likely to affect their efficiency even in quill-feathers. We 
can thus understand how it is that many of the tail-quills in 
Humming-birds, and even the wing-quills in Hulampis jugularis, 
may exhibit metallic colour and yet perform their usual function. 
But this is not the only effect produced by the difference. In Sun- 
birds the lamina is rudimentary in the metallic barbules ; now the 
lamina tends to become rudimentary in the barbules at the bases 
of the barbs, that is in downy barbules, and in the barbules at 
the apices of the barbs. Downy barbules never seem to show a 
tendeucy to become metallic, and we thus find that in Sun-birds the 
metallic barbules occur only at the ends of the barbs. A little re- 
flection will show that the consequence of this is, that the metallic 
barbules will form, a transverse band on contour-feathers, where 
the ends of the barbs stand much on the same level, and a longi- 
tudinal band on quill-feathers where the rachis is much elongated. 
The position of the bands of metallic colour on the feathers of Sun- 
birds is thus a consequence of the kind of modification to which their 
metallic barbules are subject. (See Pl. XI. fig. 1 and Pl. XII. fig. 17.) 
In Humming-birds there is an almost complete reversal of this, 
state of affairs. In them the metallic barbules have an extremely 
