154 'DESCENT OF MAN' — EXPRESSION. [1872. 



One of the additions in the sixth edition (p. 149), was a 

 reference to Mr. A. Hyatt's and Professor Cope's theory of 

 " acceleration." With regard to this he wrote (October 10, 

 1872) in characteristic words to Mr. Hyatt : — 



" Permit me to take this opportunity to express my sincere 

 regret at having committed two grave errors in the last 

 edition of my ' Origin of Species/ in my allusion to yours and 

 Professor Cope's views on acceleration and retardation of de- 

 velopment. I had thought that Professor Cope had preceded 

 you ; but I now well remember having formerly read with 

 lively interest, and marked, a paper by you somewhere in my 

 library, on fossil Cephalopods with remarks on the subject. 

 It seems also that I have quite misrepresented your joint 

 view. This has vexed me much. I confess that I have 

 never been able to grasp fully what you wish to show, and I 

 presume that this must be owing to some dulness on my 

 part." 



The sixth edition of the ' Origin ' being intended as a 

 popular one, was made to include a glossary of technical 

 terms, " given because several readers have complained . . . 

 that some of the terms used were unintelligible to them." 

 The glossary was compiled by Mr. Dallas, and being an 

 excellent collection of clear and sufficient definitions, must 

 have proved useful to many readers.] 



C. Darwin to J. L. A. de Quatrefages. 



Down, January 15, 1872. 



My DEAR Sir, — I am much obliged for your very kind 

 letter and exertions in my favour. I had thought that the 

 publication of my last book [' Descent of Man '] would have 

 destroyed all your sympathy with me, but though I estimated 

 very highly your great liberality of mind, it seems, that I 

 underrated it. 



