Alfred Russel Wallace 



producing intermediate offspring will suffice; for I know of 

 a good many varieties, which must be so called, that will 

 not blend or intermix, but produce offspring quite like either 

 parent. 



I have been particularly struck with your remarks on 

 geological distribution in Celebes. It is impossible that any- 

 thing could be better put, and [it] would give a cold shudder 

 to the immutable naturalists. 



And now I am going to ask a question which you will 

 not like. How does your Journal get on ? It will be a 

 shame if you do not popularise your researches. 



My health is so far improved that I am able to work 

 one or two hours a day. — Believe me, dear Wallace, yours 

 very sincerely, Oh. Darwin. 



9 St. Mark's Crescent, Regent's Park, N.W. February 4, 1866. 



My dear Darwin, — I am very glad to hear you are a little 

 better, and hope we shall soon have the pleasure of seeing 

 your volume on '^ Variation under Domestication." I do 

 not see the difficulty you seem to feel about two or more 

 female forms of one species. The most common or typical 

 female form must have certain characters or qualities which 

 are sufficiently advantageous to it to enable it to maintain 

 its existence ; in general, such as vary much from it die out. 

 But occasionally a variation may occur which has special 

 advantageous characters of its own (such as mimicking a 

 protected species), and then this variation will maintain 

 itself by selection. In no less than three of my polymorphic 

 species of Papilio, one of the female forms mimics the Poly- 

 dorus group, which, like the ^neas group in America, seems 

 to have some special protection. In two or three other cases 

 one of the female forms is confined to a restricted locality, 

 to the conditions of which it is probably specially adapted. 

 In other cases one of the female forms resembles the male, 



163 



