20 



some share in that immunity. This may be granted without any 

 prejudice to the question of how the resemblance or the immunity 

 arose. 



So too, in the case of the resemblance to inanimate objects, 

 and particularly to dead leaves. The protective effect of such 

 resemblance is obvious. When, however, we come back to the 

 instances where the female is simply duller or darker than the male, 

 the significance of the sexual character is not so plain. The case is 

 no doubt analogous to that of many birds, for instance those of the 

 group of pheasants, where we so often find a male of splendid 

 plumage associated with a female of comparatively dull and 

 inconspicuous colouring. Selection by the females of brilliantly- 

 coloured or peculiarly ornamental mates has, as is well known, been 

 thought to be answerable for the specially masculine attractions of 

 both birds and beasts. It is conceivable that the same principle 

 may operate among insects, and certain facts are known which lend 

 this view some support. But even so, some positive reason seems to 

 be required for the comparative dowdiness of the females. 



There is, I think, little doubt that the ruling principle here is 

 the same as in the cases of the mimicry of other insects and of the 

 resemblance to dead leaves, viz., the demand for protection. With 

 the birds that have been mentioned, the protection is afforded by 

 way of concealment. The feujale while on the nest is comparatively 

 safe from observation on account of the sober colouring of her 

 plumage, which harmonizes more or less perfectly with her 

 surroundings. The same will hold good to some extent in regard 

 to insects at rest ; but it may also be the case that inconspicuous- 

 ness, short of actual concealment, may favour the escape of the 

 dull-coloured females from the attentions of insect-eating foes. I have 

 often been struck by the fact that when the two sexes of a dimorphic 

 butterfly are flying together in some number, the eye readily picks out 

 the males as the more conspicuous, the females though perhaps equally 

 numerous, tending by comparison to escape observation. This was 

 particularly noticeable in South Africa ; the butterfly I have 

 specially in view being Bdenols sevemia, where the extra allowance 

 of dark pigment on the wings of the females certainly tended to 

 diminish the conspicuousness of that sex as compared with the 

 male ; and where also the broad dark border to the wings, almost 

 invisible during flight, caused the females to appear appreciably 

 smaller than their mates ; and, therefore, presumably less tempting 

 as objects of pursuit and capture. All this gives reason for thinking 

 that generally in these cases the aim of nature is to pay exceptional 

 attention to the preservation of the life of the female. 



The reason for this preferential dealing on the part of nature 

 has been pointed out by Alfred Russel Wallace. From the 

 point of view of the individual, no doubt the life of the male is as 

 important to Itini as that of the female is to /ler. But when we 

 regard the welfare of the species, it is plain that the life of the 



