A THEORY OF BIRDS' NESTS, 251 
Exceptional Cases confirmatory of the above 
Explanation. 
There exist a few very curious and anomalous facts 
in the natural history of birds, which fortunately serve 
as crucial tests of the truth of this mode of explaining 
the inequalities of sexual colouration. It has been long 
known, that in some species the males either assisted in, 
‘or wholly performed, the act of incubation. It has also 
been often noticed, that in certain birds the usual sexual 
differences were reversed, the male being the more 
plainly coloured, the female more gay and often larger. 
I am not, however, aware that these two anomalies had 
ever been supposed to stand to each other in the rela- 
tion of cause and effect, till I adduced them in support 
of my views of the general theory of protective adapta- 
tion. Yet it is undoubtedly the fact, that in the best 
known cases in which the female bird is more conspi- 
cuously coloured than the male, it is either positively 
ascertained that the latter performs the duties of in- 
cubation, or there are good reasons for believing such 
tobe the case. The most satisfactory example is that 
of the Gray Phalarope (Phalaropus fulicarius), the 
sexes of which are alike in winter, while in summer 
the female instead of the male takes on a gay and 
conspicuous nuptial plumage; but the male performs 
the duties of incubation, sitting upon the eggs, which 
are laid upon the bare ground. 
In the Dotterell (Eudromias morinellus) the female 
is larger and more brightly coloured than the male; and 
