464 
NATURE 
[April 13, 1871 

be their peculiar attractions, in order to gain the same 
end. This rule is confirmed by the exceptional case of 
the cassowary and a few other species in which the hens 
court the male birds, fight together in rivalry, and ac- 
cordingly assume the brighter colours and more attrac- 
tive shape usually worn by the male. Not only the 
parental and incubating instincts, but the usual moral 
qualities of the two sexes are in these cases reversed : “the 
females being savage, quarrelsome, and noisy, the males 
gentle and good.” But it is further necessary to show that 
the females exert a choice among the males, and that the 
latter are polygamous, or arrive earlier at the place of 
pairing, as is the case with some birds, or else exceed in 
numbers, at least when both sexes are mature. On this 
point a series of observations is recorded relating chiefly 
to man, to domesticated mammals, and to insects. The 
rule as to transmission of male characters to both sexes 
appears to be that when variations appear late in life they 
are usually developed in the same sex only of the next 
generation, although they are, of course, transmitted in 
a latent condition through both; while, on the other 
hand, the differences which appear before maturity in the 

Fic. 2.—Chameieon Owenit. Upper figure, male ; lower figure, female. 
parent are equally developed in both sexes when trans- 
mitted to the offspring. The numerous apparent ex- 
ceptions to these laws of inheritance and of sexual 
selection are examined with wonderful fairness and fer- 
tility in resource. I may particularly refer to the dis- 
cussion of the ways in which the young and adults of 
both sexes differ among birds. The extreme intricacy of 
some of the questions considered is best shown by a 
postscript in which, with characteristic candour, the author 
corrects ‘‘a serious and unfortunate error” in the eighth 
chapter. 
The remainder of the first and the greater portion of | 
second volume are occupied by a survey of sexual 
variations throughout the animal kingdom. Passing 
rapidly over the other invertebrate classes, the author 
devotes two chapters to the secondary sexual characters 
of insects. The weapons, the ornaments, and the sounds 
peculiar to the males of this vast group of animals are 
briefly described, and the remarkable analogy between 
insects and birds which is seen in so many other particulars 
is traced here also. The brilliant colours of many cater- 
pillars, which, of course, cannot be due to sexual selection, 
offer one of the many difficulties which are faced, and this 

is explained by the aid of what the author terms Mr. 
Wallace’s “ innate genius for solving difficulties,” as being 
due to natural selection. The bright cclours warn the 
enemies of the caterpillars that they are unfit for food, and 
so benefit the latter, “on nearly the same principle that 
certain poisons are coloured by druggists for the good of 
man.” Many cases are probably further complicated by 
mimicry, savoury caterpillars assuming the colours of 
distasteful ones so as to share in their immunity, in the 
same way that a druggist might label his bottles of sweet- 
meats “ poison,” to keep them from the shop-boy. 
In the frigid classes of the lower Vertebrata one would 
think that sexual selection would have little play ; yet Mr. 
Darwin gives several instances among fishes, amphibians, 
and reptiles in which weapons or ornaments, peculiar to 
the males, appear to have been acquired by this means. 
(See Fig. 2.) But it is in the great class of birds that 
the most complete series of examples is found, and our 
advanced knowledge of the habits of this class renders it 

Fic. 3.—Head of Semmnopithecus rubicundus. This figure (from Prof, 
Gervais) is given to show the odd arrangement and development of the 
hair on the head. 
the best possible field for the exposition of the whole 
theory. Again and again our author forestalls the evidence 
adduced in the chapters on sexual selection among birds, 
when tracing its first obscure operation among lower 
classes, and falls back on the same stronghold when ex- 
plaining its less obvious working in the mammalia. 
Among birds the rivalry of beauty has led to far 
more striking results than has the rivalry of strength. 
Foremost of these is the power of song, which, in 
accordance with the law of the least waste, is usually 
confined to birds of inconspicuous colours, while 
the combination of the harsh note with the magni- 
ficent plumage of the peacock is a familiar converse 
example. The object of the adornment of birds is con- 
clusively proved by its being, as a rule, confined to males, 
and often to them only during the breeding season, as well 
