1870.] DR. GUNTHER'S HELP. 1 23 



classes I am astonished to find how similar the rules are about 

 the nuptial or " wedding dress " of all animals. The subject 

 has begun to interest me in an extraordinary degree ; but I 

 must try not to fall into my common error of being too 

 speculative. But a drunkard might as well say he would 

 drink a little and not too much ! My essay, as far as fishes, 

 batrachians and reptiles are concerned, will be in fact yours, 

 only written by me. With hearty thanks, 



Yours very sincerely, 



Ch. Darwin. 



[The following letter is of interest, as showing the excessive 

 care and pains which my father took in forming his opinion 

 on a difficult point :] 



C. Darwin to A. R. Wallace. 



Down, September 23 [undated]. 



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 re-written 

 some pages you would know how anxious I am to arrive as 

 near as I can to the truth. 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 is 

 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 y 

 could come to be transmitted to males alone. It is not 

 enough that females should be produced from the males 

 with red feathers, which should be destitute of red feathers ; 

 but these females must have a latent tendency to produce 

 such feathers, otherwise they would cause deterioration 

 in the red head-feathers of their male offspring. Such 



