120 ALEXANDER AGASSIZ 



more one is adrift to get a correct diagnosis of a genus 

 or a species, and the gradual passage in Echini of the 

 most widely separated groups leaves in my mind but 

 little doubt that our classification is nothing but the 

 most arbitrary convenient tool, depending upon the ma- 

 terial at our command at a special time. The generali- 

 zations to which I am led from the careful study of such 

 a small group as the Echini I shall publish at the end 

 of my "Revision of the Echini" and as the Plates for the 

 descriptive part are far advanced, I hope I shall not be 

 long delayed. We have excellent news from the Hassler 

 Expedition from Rio. Not much was expected from 

 the dredging on this side of Cape Horn owing to the 

 lateness of the season, but the single haul made off the 

 Barbados must have been a wonderful catch of which 

 I trust we shall hear and see more by and by. 



TO DARWIN 



Cambridge, Dec. 9, 1872. 

 I have to thank you for the trouble you have taken 

 in sending me a copy of your " Expression of the Emo- 

 tions," which has duly come to hand. I have not had 

 a moment to look into it, in part on account of the work 

 of distributing some collections which have lately ar- 

 rived, and in part owing to the great fire which has 

 devastated Boston, and which has affected us all more 

 or less seriously. I have been hit pretty hard, not in a 

 money way, but what is worse infinitely, I have lost a 

 year's work by the destruction of six Plates of anatomy 

 with the original drawings, of which I have not even 

 a sketch. They had been sent to Boston the morning 

 of the fire to be lettered preparatory to printing. In 

 addition I lost all the stones of the first parts of the 



