344 EVOLUTION [CHAP. V 



Letter 254 conditions, and that when the species were verging towards 

 extinction (owing probably to the presence of some more 

 successful competitors) they would naturally become re- 

 adapted to simpler conditions. Before I had read your final 

 remarks I thought also that unfavourable conditions might 

 cause, through the law of growth, aided perhaps by reversion, 

 degradation of character. No doubt many new laws re- 

 main to be discovered. Permit me to add that I have 

 never been so foolish as to imagine that I have succeeded in 

 doing more than to lay down some of the broad outlines of 

 the origin of species. 



After long reflection I cannot avoid the conviction that no 

 innate tendency to progressive development exists, as is now 

 held by so many 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 x 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 researches. 



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. 2 



Letter 255 A. Hyatt to C. Darwin. 



Cannstadt bei Stuttgart, Dec. 8th, 1872. 



The quickness and earnestness of your reply to my letter 

 gives me the greatest encouragement, and I am much 

 delighted at the unexpected interest which your questions 

 and comments display. What you say about Prof. Cope's 

 style has been often before said to me, and I have remarked 

 in his writings an unsatisfactory treatment of our common 



1 Hilgendorf, Monatsb. K. Akad., Berlin, 1866. For a semi-popular 

 account of Hilgendorf s and Hyatt's work on this subject, see Romanes' 

 Darivi?i and after Darwin, I., p. 201. 



2 See various papers in the publications of the Boston Soc. Nat. Hist. 

 and in the Bulletin of the Harvard Museum of Comp. Zoology. 



