Remember me kindly to all my Zurich friends, and especially to Arnold Escher. . . Agassiz's increasing and at last wholly unmanageable correspondence attests the general sympathy for and cooperation with his scientific aims in the United States. In 1853, for instance, he had issued a circular, asking for collections of fishes from various fresh-water systems of the United States, in order that he might obtain certain data respecting the laws of their distribution and localization. To this he had hundreds of answers coming from all parts of the country, many of them very shrewd and observing, giving facts respecting the habits of fishes, as well as concerning their habitat, and offering aid in the general object. Nor were these empty promises. A great number and variety of collections, now making part of the ichthyological treasures of the Museum at Cambridge, were forwarded to him in answer to this appeal. Indeed, he now began to reap, in a new form, the harvest of his wandering lecture tours. In this part of his American experience he had come into contact with all classes of people, and had found some of his most intelligent and sympathetic listeners in the working class. Now that he needed their assistance he often found his co-laborers among farmers, stock-raisers, sea-faring men, fishermen, and sailors. Many a New England captain, when he started on a cruise, had on board collecting cans, furnished by Agassiz, to be filled in distant ports or nearer home, as the case might be, and returned to the Museum at Cambridge. One or two letters, written to scientific friends at the time the above-mentioned circular was issued, will give an idea of the way in which Agassiz laid out such investigations. TO JAMES D. DANA. CAMBRIDGE, July 8, 1853. . . .I have been lately devising some method of learning how far animals are truly autochthones, and how far they have extended 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 will for the present limit myself to the fresh-water fishes and shells, and for the sake of comparison I will try to collect carefully all the species living in the rivers of Connecticut, New York, and New Jersey, and see whether they are identical with those of the island. Whatever may come out of such an investigation it will, at all events, furnish interesting data upon the local distribution of the species. . .I am almost confident that it will lead to something interesting, for there is one feature of importance in the case; the present surface of Long Island is not older than the drift period; all its inhabitants must, therefore, have been introduced since that time. I shall see that I obtain similar collections from the upper course of the Connecticut, so as to ascertain whether there, as in the Mississippi, the species differ at different heights of the river basin. . . TO PROFESSOR S.S. HALDEMAN, COLUMBIA, PENNSYLVANIA.