208 The Naturalist in La Plata. 
for representation, meets the light at the requisite 
angle, and that point alone should be shown in full 
brilhance cf colour. A flowery shrub is sometimes 
seen surrounded by a cloud of humming-birds, all 
of one species, and each, of course, in a different 
position. If someone would draw such a scene 
as that, showing a different detail of colour in each 
bird, according to its position, then some idea of 
the actual appearance of the bird might be given 
to one who had never seen an example.” 
It is hardly to be expected that anyone will carry 
out the above suggestion, and produce a monograph 
with pages ten or fifteen feet wide by eighteen feet 
long, each one showing a cloud of humming-birds 
of one species flitting about a flowery bush; but 
even in such a picture as that would be, the birds, 
suspended on unlovely angular projections instead 
of ‘“‘hazy semicircles of indistinctness,’ and each 
with an immovable fleck of brightness on the other- 
wise sombre plumage, would be as unlike living 
humming-birds as anything in the older mono- 
eraphs. 
Whether the glittering iridescent tints and 
singuiar ornaments for which this family is famous 
result from the cumulative process of conscious or 
voluntary sexual selection, as Darwin thought, 
or are merely the outcome of a superabundant 
vitality, as Dr. A. R. Wallace so strongly maintains, 
is a question which science has not yet answered 
satisfactorily. ‘lhe tendency to or habit of varying 
in the direction of rich colouring and beautiful or 
fantastic ornament, might, for all we know to the 
contrary, have descended to humming-birds from 
