250 The Naturalist in La Plata. 
patch, the throat thus having three strongly con- 
trasted colours, arranged in four divisions. The 
presence of this bright throat spot in so many 
species cannot very well be attributed to voluntary 
sexual selection, although believers in that theory 
are of course at liberty to imagine that when en- 
gaged in courtship, the male bird, or rather male 
and female both, as both sexes possess the spot, 
hold up their heads vertically to exhibit it. Per- 
haps it would be safer to look on it as a mere 
casnal variation, which, like the exquisitely pencilled 
feathers and delicate tints on the concealed sides 
and under surfaces of the wings of many species 
possessing outwardly an obscure protective colour- 
ing, is neither injurious nor beneficial in any way, 
either to the birds or to the theory. It is more 
than probable, however, that in such small feeble- 
winged, persecuted birds, this spot of colour would 
prove highly dangerous on any conspicuous part of 
the body. In some of the more vigorous, active 
species, we can see a tendency towards a brighter 
colouring on large, exposed surfaces. In Auto- 
malus the tail is bright satiny rufous; in Pseudo- 
colaptes the entire under surface is rufous of a 
peculiar vivid tint, verging on orange or red; in 
Magarornis the bosom is black, and _ beautifully 
ornamented with small leaf-shaped spots of a 
delicate straw-colour. There are several other 
very pretty birds in this homely family; but the 
finest of all is Thripodectes flammulatus, the whole 
body being tortoise-shell colour, the wings and tail 
bright chesnut. The powerful tanager-like beak of 
this species seems also to show that it has diverged 
