Or perhaps the protection is acquired because this tendency exists.  I admit therefore in the case of concealed nests they [habits] may have been acquired for protection.

Now for the special case.

7.  In the very weak-flying Leptalis both sexes mimic Heliconidae.

8.  In the much more powerful Papilio, Pieris, and Diadema it is generally the female only that mimics Danaida.

9.  In these cases the females often acquire more bright and varied colours than the male.  Sometimes, as in Pieris pyrrha, conspicuously so.

10.  No single case is known of a male Papilio, Pieris, Diadema (or any other insect?) alone mimicking a Danais, etc.

11.  But colour is more frequent in males, and variations always seem ready for purposes of sexual or other selection.

12.  The fair inference seems to be that given in proposition 5 of the general argument, viz. that each species and each sex can only be modified by selection just as far as is absolutely necessary, not a step farther.  A male, being by structure and habits less exposed to danger and less requiring protection than the female, cannot have more protection given to it by Natural Selection, but a female must have some extra protection to balance the greater danger, and she rapidly acquires it in one way or another.

13.  An objection derived from cases like male fish, which seem to require protection, yet having brighter colours, seems to me of no more weight than is that of the existence of many white and unprotected species of Leptalis to Bates’s theory of mimicry, that only one or two species of butterflies perfectly resemble leaves, or that the instincts or habits or colours that seem essential to the preservation of one animal are often totally absent in an allied species.

* * * * *

Down, Bromley, Kent.  September 23, 1868.

My dear Wallace,—­I am very much obliged for all your trouble in writing me your long letter, which I will keep by me and ponder over.  To answer it would require at least 200 folio pages!  If you could see how often I have rewritten some pages, you would know how anxious I am to arrive as near as I can to the truth.  We differ, I think, chiefly from fixing our minds perhaps too closely on different points, on which we agree:  I lay great stress on what I know takes place under domestication:  I think we start with different fundamental notions on inheritance.  I find it most difficult, but not, I think, impossible, to see how, for instance, a few red feathers appearing on the head of a male bird, and which are at first transmitted to both sexes, could come to be transmitted to males alone;[72] but I have no difficulty in making the whole head red if the few red feathers in the male from the first tended to be sexually transmitted.  I am quite willing to admit that the female may have been modified,