Introduction : V ariation. 
67 
female is also easily to be understood on the ground of the elimination of the 
disadvantageoiisly coloured birds of this sex, yet the explanation ^oes not seem 
to apply to the majority of cases, in many of which the female is like the male, 
and in others she is only a little less bright or wants some special mai ing 
and appears then to represent a lower stage in the history of the lace, a 
immature male is often like her. Many males assist in incubation, ihe female 
of the Cuckoo, Eudynamk, which lays its eggs in Crows’ nests does not appea 
to be protectively coloured, but the male, being black, might be thought to be so. 
Darwin’s theory of sexual selection has been much contested of late years. 
The author cites cases of certain female bmls in captivity mating by preference 
with certain males and avoiding others; though allowance must perhaps be marie 
for this in nature, there is now a strong opinion in favour o t e vie 
passive role being generally played by the female, the male expelling his rivals 
and making the female yield to him. 
There i, much to be ..id for Mr. W.llace'. view of an exces. of rtah^ 
or growth-force in the male as the cause of the development 
decorative plumes, etc., though a localization of such grow s m . ‘ 
centres of high nervous or muscular activity” is not tenaWe. lor 
second primary of the male “"^'“"hree^loig ’racket-feathers 
into an enormous racket-feather capable of erection, g nee 
sprout from each side of the head of the male of the ara ise ir , „ 
very long one in Pteridophora, etc., etc. As the principa muscu ar a 
centres are not different in birds, such a great diversity m t e 
accessory growths could not arise from this cause. Why does t e ma e 
have its ornamentation chiefly on the side of the bi east, and ano 
Paradise, Lophorhina, on the occipital region and jugulum? 
Mr. Wallace’s theory appears to include “the normal deve opmen o co 
due to the complex chemical and structural changes ever .^Tryf-ii- 
organism” (Darwinism, p. 288}, for the sex which possesses the most 
■force will be the first to undergo these necessary rnodmcations^^ ypiooLntal 
that a great number of sexual differences owe their origin to this developmental 
Mv.1l"n ;ra^s lb’’ .w„ se.xes as naluvally lnlm« lo »e 
well-being. The males above a certam number meje^e^pm 
the food-supply and persecute the fema , m-oduces males which 
of male offspring, and We are unable to 
are disastrously equipped for the sti gs annears to us that the 
grasp the argument, if indeed it is ^ which will per- 
handicapped males wi be the i^^ best-equipped 
petuate i„ierited, these males will somewhat counteract 
offspring. Then ^ahties ^g^^ ^ 
Ltter“erate will be less likely to survive than their sisters. As their inferior 
