78 NATURAL SELECTION III 
same district, whereas allied forms of every degree of nearness 
and remoteness generally inhabit different countries, and 
often different quarters of the globe; and neither it nor 
“similar conditions” will account for the likeness between 
species of distinct groups being superficial only—a disguise, 
not a true resemblance ; for the imitation of bark, of leaves, 
of sticks, of dung; for the resemblance between species in 
different orders, and even different classes and sub-kingdoms ; 
and finally, for the graduated series of the phenomena, 
beginning with a general harmony and adaptation of tint in 
autumn and winter moths and in arctic and desert animals, 
and ending with those complete cases of detailed mimicry 
which not only deceive predacious animals, but puzzle the 
most experienced insect collectors and the most learned 
entomologists. 
Mimicry by Female Insects only 
But there is yet another series of phenomena connected 
with this subject, which considerably strengthens the view 
here adopted, while it seems quite incompatible with either 
of the other hypotheses; namely, the relation of protective 
colouring and mimicry to the sexual differences of animals. 
It will be clear to every one that if two animals, which as 
regards “external conditions” and “hereditary descent” are 
exactly alike, yet differ remarkably in coloration, one 
resembling a protected species and the other not, the resem- 
blance that exists in one only can hardly be imputed to the 
influence of external conditions or as the effect of heredity. 
And if, further, it can be proved that the one requires 
protection more than the other, and that in several cases it is 
that one which mimics the protected species, while the one 
that least requires protection never does so, it will afford 
very strong corroborative evidence that there is a real con- 
nection between the necessity for protection and the pheno- 
menon of mimicry. Now the sexes of insects offer us a test 
of the nature here indicated, and appear to furnish one of 
the most conclusive arguments in favour of the theory that 
the phenomena termed “mimicry” are produced by natural 
selection. 
The comparative importance of the sexes varies much in 
