LETTERS OF CHARLES DARWIN. 411 



to disturb and break their eggs much. With respect to the females 

 of deer not having horns, I presume it is to save the loss of organised 

 matter. In your note you speak of sexual selection and protection as 

 sufficient to account for the colouring of all animals, but it seems to 

 me doubtful how far this will come into play with some of the lower 

 animals, such as sea anemones, some corals, etc., etc. On the other 

 hand Hackel has recently well shown that the transparency and ab- 

 sence of colour in the lower oceanic animals, belonging to the most 

 different classes, may be well accounted for on the principle of pro- 

 tection. 



Some time or other I should like much to know where your paper 

 on the nests of birds has appeared, and I shall be extremely anxioUd 

 to read your paper in the Westminster Review. Your paper on the 

 sexual colouring of birds will, I have no doubt, be very striking. For- 

 give me, if you can, for a touch of illiberality about your paper. 



To Aug. Weismann. 



Down, Feb. 29th, 1872. 

 I am rejoiced to hear that your eyesight is somewhat better; but I 

 fear that work with the microscope is still out of your power. I have 

 often thought with sincere s}rmpathy how much you must have suffered 

 from your grand line of embryological research having been stopped. 

 It was very good of you to use your eyes in writing to me. I have just 

 received your essay; but as I am now staying in London for the sake 

 of rest, and as German is at all times very difficult to me, I shall not 

 be able to read your essay for some little time. I am, however, very 

 curious to learn what you have to say on isolation and on periods of 

 variation. I thought much about isolation when I wrote in Chapter 

 IV. on the circumstances favourable to Natural Selection. No doubt 

 there remains an immense deal of work to do on 'Artbildung. ' I have 

 only opened a path for others to enter, and in the course of time to 

 make a broad and clear high-road. I am especially glad that you are 

 turning your attention to sexual selection. I have in this country 

 hardly found any naturalists who agree with me on this subject, even 

 to a moderate extent. They think it absurd that a female bird should 

 be able to appreciate the splendid plumage of the male; but it would 

 take much to persuade me that the peacock does not spread his gorgeous 

 tail in the presence of the female in order to fascinate or excite her. 

 The case, no doubt, is much more difficult with insects. I fear that 

 you will find it difficult to experiment on diurnal lepidoptera in con- 

 finement, for I have never heard of any of these breeding in this state. 

 I was extremely pleased at hearing from Fritz Muller that he liked my 

 chapter on lepidoptera in the Descent of Man more than any other 

 part, excepting the chapter on morals. 



