LETTERS OF CHARLES DARWIN. 405 



able naturalists, and perhaps by yourself. It is curious how seldom 

 writers define what they mean by progressive development; but this 

 is a point which I have briefly discussed in the Origin. I earnestly 

 hope that you may visit Hilgendorf s famous deposit. Have you seen 

 Weismann's pamphlet Einfluss der Isolirung, Leipzig, 1872? He 

 makes splendid use of Hilgendorf 's admirable observations. I have 

 no strength to spare, being much out of health; otherwise I would 

 have endeavoured to have made this letter better worth sending. I 

 most sincerely wish you success in your valuable and difficult re- 

 searches. 



I have received, and thank you, for your three pamphlets. As far 

 as I can judge, your views seem very probable; but what a fearfully 

 intricate subject is this of the succession of ammonites. 



To B. D. Walsh. 



Down, Dec. 4th [1864]. 



I have been greatly interested by your account of your American 

 life. What an extraordinary and self-contained life you have led ! 

 and what vigour of mind you must possess to follow science with so 

 much ardour after all that you have undergone ! I am very much 

 obliged to you for your pamphlet on Geographical Distribution, on 

 Agassiz, etc. I am delighted at the manner in which you have bearded 

 this lion in his den. I agree most entirely with all that you have 

 written. What I meant when I wrote to Agassiz to thank him for a 

 bundle of his publications, was exactly what you suppose. I confess, 

 however, I did not fully perceive how he had misstated my views; but 

 I only skimmed through his Methods of Study, and thought it a very 

 poor book. I am so much accustomed to be utterly misrepresented that 

 it hardly excites my attention. But you really have hit the nail on the 

 head capitally. All the younger good naturalists whom I know think 

 of Agassiz as you do; but he did grand service about glaciers and fish. 

 About the succession of forms, Pictet has given up his whole views, 

 and no geologist now agrees with Agassiz. I am glad that you have 

 attacked Dana's wild notions; [though] I have a great respect for 

 Dana. ... If you have an opportunity, read in Trans. Linn. Soc. 

 Bates on 'Mimetic Lepidoptera of Amazons.' I was delighted with 

 his paper. 



I have got a notice of your views about the female Cynips inserted 

 in the Natural History Review: whether the notice will be favourable, 

 I do not know; but anyhow it will call attention to your views. . . . 



As you allude in your paper to the believers in change of species, 

 you will be glad to hear that very many of the very best men are coming 

 round in Germany. I have lately heard of Hackel, Gegenbauer, F. 



