1868. ] Zoology. 429 
the result of a variety of causes, which have been continually 
inducing modification, in accordance with changed organic or phy- 
sical conditions, v2z. first, the structure of the species; and second, 
its environment. He further points out that these are correlative, 
the former cause depending upon the latter, and not vice versa. 
Mr. Wallace lays it down as a rule, that when both sexes of birds 
are of strikingly gay and conspicuous colours, the nest is such as to 
conceal the sittmg bird ; while whenever there is a striking contrast 
of colours (the male being gay and conspicuous, the female dull and 
obscure), the nest is open and the sitting bird exposed to view. He 
gives many illustrations of this view, embracing almost every group 
of bright-coloured birds. Mr. Wallace says he was first led to see 
these relations by the study of protective resemblance or mimicry 
among insects, and points out that there is no incapacity in the 
female sex among birds to receive the same bright hues and strongly 
contrasted tints with which their partners are so often decorated, 
since whenever they are protected or concealed during incubation, 
they are so adorned: hence, he infers, that it is due to the absence 
of such concealment that gay and conspicuous tints are withheld, as 
in the Chatterers, Manakins, and Tanagers. A few anomalous facts 
supply a crucial test, vz. in cases where the males assist in incuba- 
tion, or perform it altogether, in which case, as in the Grey Phala- 
rope, the sexes, which are alike in winter, become reversed in colours 
in summer, the female instead of the male taking on a gay and 
nuptial plumage—while the male sits on the eggs, which are laid 
upon the bare ground. 
A curious instance of misplacement, for want of sufficient speci- 
mens for examination, seems likely to be corrected, in the case of a 
bird (Steatornis caripensis), referred to the goat-suckers from out- 
ward resemblance, but which is known to feed on fruits so hard as 
to require a hammer to break them. Specimens have lately been 
received in spirits, and presented to the College of Surgeons and 
British Museum, which will be submitted to anatomical examination. 
Sexes of Spiders—Mr. Pickard-Cambridge remarks upon the 
numerical relations between the sexes of spiders. He says that in 
the extensive group Epéiride, comprising several genera, he has 
never seen an example of the male sex; nor in an examination of 
the Museums of Vienna, Milan, Berlin, Frankfort, and Leyden, 
could he meet with a specimen, though females occurred in them 
all. He supposes that the males of this group are exceedingly 
small compared to females, and probably overlooked by collectors— 
and probably they would look like little horny and more or less 
spiny ticks. In Nephila, which are giants of the spider race, the 
males are almost unknown, and when known are ridiculously dis- 
proportionate in size to the females. Some species of other families 
also present a striking disproportion in the relative size of the sexes. 
