358 'DESCENT OF MAN 'EXPRESSION. [1873. 



The following letter refers inter alia to a letter which 

 appeared in 'Nature' (Sept. 25, 1873), "On the Males and 

 Complemental Males of certain Cirripedes, and on Rudi- 

 mentary Organs :"] 



C. Darwin to E. HaeckeL 



Down, September 25, 1873. 



MY DEAR HACKEL, I thank you for the present of your 

 book,* and I am heartily glad to see its great success. You 

 will do a wonderful amount of good in spreading the doctrine 

 of Evolution, supporting it as you do by so many original 

 observations. I have read the new preface with very great 

 interest. The delay in the appearance of the English trans- 

 lation vexes and surprises me, for I have never been able to 

 read it thoroughly in German, and I shall assuredly do so 

 when it appears in English. Has the problem of the later 

 stages of reduction of useless structures ever perplexed you ? 

 This problem has of late caused me much perplexity. I have 

 just written a letter to ' Nature ' with a hypothetical explana- 

 tion of this difficulty, and I will send you the paper with the 

 passage marked. I will at the same time send a paper which 

 has interested me ; it need not be returned. It contains a 

 singular statement bearing on so-called Spontaneous Gener- 

 ation. I much wish that this latter question could be settled, 

 but I see no prospect of it. If it could be proved true this 

 would be most important to us. ... 



Wishing you every success in your admirable labours, 

 I remain, my dear Hackel, yours very sincerely, 



CHARLES DARWIN. 



* ' Schopfungs-geschichte,' 4th ed. The translation (' The History of 

 Creation ') was not published until 1876. 



