LIFE OF JAMES DWIGHT DANA 

 AGASSIZ TO DANA 



How Far are A nimals A boriginal f 



" CAMBRIDGE, July 8, 1853. 



" I have never felt more keenly than I do now, since 

 my inability to work hard leaves me time for writing let- 

 ters, how much I have lo'st by not attempting to keep up 

 a regular correspondence with you. I was delighted to- 

 day to learn from you that you are satisfied that genera 

 are not mere artful devices of naturalists to register their 

 observations upon species. You are the first naturalist 

 I have found who had that confidence ; but, as you say, 

 it requires more knowledge to arrive at that conviction 

 than most of our zoologists possess. To me genera ap- 

 pear like general portions in the mind of the Creator, of 

 which species are only the different expressions. But 

 who would grant that except those who recognize in 

 nature the thought of a personal God ? You are not so 

 much at leisure now as I am obliged to be, so do not 

 think that I expect an answer to all my notes, but grant 

 me the pleasure to write as often as you can. I have 

 been lately devising some method to ascertain how far 

 animals are truly autochtone and how far they have ex- 

 tended their primitive boundaries. I will attempt to test 

 that question with Long Island, the largest of all the 

 islands along our coast. For this purpose I would for 

 the present limit myself to the fresh-water fishes and shells, 

 and for the sake of comparison collect carefully all the 

 species living in the rivers of Connecticut, New York, and 

 New Jersey, and ascertain whether they are identical 

 with those of the island. Whatever may come out of 

 such an investigation, it will at all events furnish interest- 

 ing data upon the local distribution of the species. Could 

 you for this object give me names of some gentlemen 

 they need not be naturalists who could undertake to put 

 up for me, in alcohol, all the fishes and shells found 

 above tide-level in Thames River and its tributaries, in 

 the Connecticut, Farmington River, Housatonic, and any 

 watercourse upon which you may chance to have intelli- 

 gent and obliging acquaintances ? I have already applied 

 to New York and New Jersey, and I am almost confident 



322 



