The Wallace-Darwin Correspondence 



and perhaps receives a protection from the abundance of the 

 males, in the crowd of which it is passed over. I think these 

 considerations render the production of two or three forms 

 of female very conceivable. The physiological difficulty is 

 to me greater, of how each of two forms of female produces 

 offspring like the other female as well as like itself, but no 

 intermediates ? 



If you ** know varieties that will not blend or intermix, 

 but produce offspring quite like either parents," is not that 

 the very physiological test of a species which is wanting for 

 the complete proof of the origin of species ? 



I have by no means given up the idea of writing my 

 Travels, but I think I shall be able to do it better for the 

 delay, as I can introduce chapters giving popular sketches 

 of the subjects treated of in my various papers. 



I hope, if things go as I wish this summer, to begin work 

 at it next winter. But I feel myself incorrigibly lazy, and 

 have no such system of collecting and arranging facts or 

 of making the most of my materials as you and many of 

 our hard-working naturalists possess in perfection. — With 

 best wishes, believe me, dear Darwin, yours most sincerely, 



Alfred R. Wallace. 

 Down J Bromley, 8.E. Tuesday, Febmary, 1866. 



My dear Wallace, — After I had dispatched my last note, 

 the simple explanation which you give had occurred to me, 

 and seems satisfactory. I do not think you understand what 

 I mean by the non-blending of certain varieties. It does not 

 refer to fertility. An instance will explain. I crossed the 

 Painted Lady and Purple sweet peas, which are very differ- 

 ently coloured varieties, and got, even out of the same pod, 

 both varieties perfect, but none intermediate. Something 

 of this kind, I should think, must occur at first with your 

 butterflies and the three forms of Lythrum; though these 



m 



