The difficulty of carrying out comparisons so rigorous and extensive as were needed in order to reconstruct the organic relations between the fossil fishes of all geological formations and those of the present world, is best told by the author.* (* "Recherches sur les Poissons Fossiles" volume 1. Addition a la Preface.) "Possessing no fossil fishes myself, and renouncing forever the acquisition of collections so precious, I have been forced to seek the materials for my work in all the collections of Europe containing such remains; I have, therefore, made frequent journeys in Germany, in France, and in England, in order to examine, describe, and illustrate the objects of my researches. But notwithstanding the cordiality with which even the most precious specimens have been placed at my disposition, a serious inconvenience has resulted from this mode of working, namely, that I have rarely been able to compare directly the various specimens of the same species from different collections, and that I have often been obliged to make my identification from memory, or from simple notes, or, in the more fortunate cases, from my drawings only. It is impossible to imagine the fatigue, the exhaustion of all the faculties, involved in such a method. The hurry of traveling, joined to the lack of the most ordinary facilities for observation, has not rendered my task more easy. I therefore claim indulgence for such of my identifications as a later examination, made at leisure, may modify, and for descriptions which sometimes bear the stamp of the precipitation with which they have been prepared." It was, perhaps, this experience of Agassiz's earlier life which made him so anxious to establish a museum of comparative zoology in this country,--a museum so abundant and comprehensive in material, that the student should not only find all classes of the animal kingdom represented within its walls, but preserved also in such numbers as to allow the sacrifice of many specimens for purposes of comparison and study. He was resolved that no student should stand there baffled at the door of knowledge, as he had often done himself, when shown the one precious specimen, which could not be removed, or even examined on the spot, because unique. CHAPTER 8. 1834-1837: AGE 27-30. First Visit to England. Reception by Scientific Men. Work on Fossil Fishes there. Liberality of English Naturalists. First Relations with American Science. Farther Correspondence with Humboldt. Second Visit to England. Continuation of "Fossil Fishes." Other Scientific Publications. Attention drawn to Glacial Phenomena. Summer at Bex with Charpentier. Sale of Original Drawings for "Fossil Fishes." Meeting of Helvetic Society. Address on Ice-Period. Letters from Humboldt and Von Buch.