338 EVOLUTION [Chap. V 



Letter 251 species ! I daresay you have thought of experimenting on 

 the mental powers of the spiders by fixing their trap-doors 

 open in different ways and at different angles, and observing 

 what they will do. 



We have been here some days, and intend staying some 

 weeks ; for I was quite worn out with work, and cannot be 

 idle at home. 



I sincerely hope that your health is not worse. 



Letter 252 To A. Hyatt. 1 



The correspondence with Professor Hyatt, of Boston, U.S., originated 

 in the reference to his and Professor Cope's s theories of acceleration and 

 retardation, inserted in the sixth edition of the Origin, p. 149. 



Mr. Darwin, on receiving from Mr. Hyatt a copy of his "Fossil 

 Cephalopods of the Museum of Comparative Zoology. Embryology," 

 from the Bull. Mus. Cemp. Zoo!., Harvard, Vol. III., 1872, wrote as 



follows 3 : — „ 



Oct. 10th, 1872. 



I am very much obliged to you for your kindness in 



having sent me your valuable memoir on the embryology of 



the extinct cephalopods. The work must have been one of 



immense labour, and the results are extremely interesting. 



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 



1 Alpheus Hyatt (1838-1902) was a student under Louis Agassiz, to 

 whose Laboratory he returned after serving in the Civil War, and under 

 whom he began the researches on Fossil Cephalopods for which he is 

 so widely known. In 1867 he became one of the Curators of the Essex 

 Institute of Salem, Mass. In 1870 he was made Custodian, and in 1881 

 Curator of the Boston Society of Natural History. He held profes- 

 sorial chairs in Boston University and in the Massachusetts Institute of 

 Technology, "and was at one time or another officially connected with 

 the Museum of Comparative Zoology and the United States Geological 

 Survey." See Mr. S. Henshaw (Science, XV, p. 300, Feb. 1902), where 

 a sketch of Mr. Hyatt's estimable personal character is given. See also 

 Prof. Dall in the Popular Science Monthly, Feb. 1902. 



3 Edward Drinker Cope (1840-97) was for a short time Professor at 

 Haverford College ; he was a member of certain United States Geolo- 

 gical Survey expeditions, and at the time of his death he held a 

 Professorship in the University of Pennsylvania. He wrote several 

 important memoirs on " Vertebrate Paleontology," and in 18S7 published 

 The Origin of the Fit lest. 



:1 Part of this letter was published in Life and Letters, III., p. 154. 



