Returning from Paris, Agassiz lectured on natural history subjects in his native country. His exceptional ability attracted the interest of scientific men throughout Europe and he received many honors and complimentary invitations. In 1833 he married the sister of his intimate friend, Alexander Braun, the botanist. The art of his wife in drawing and coloring illustrations for his volumes on fishes was of the greatest assistance to him. In the years that immediately followed his marriage, Agassiz became interested in glacial research and was an important member of extended summer explorations in the Alps. His theories relating to the structure of glaciers were incorporated in a book entitled "_Système Glaciare_." Having for some time desired to continue his researches in the United States, it was with delight that he received in 1846 an invitation to give a course of lectures in Boston. As a lecturer he met with such brilliant success that he was subsequently appointed professor of natural history at Harvard. From this time until his death in 1873, Professor Agassiz was identified with the cause of science in the United States. His work as a teacher was supplemented by repeated excursions to various parts of the continent with the object of studying forests, geological formations and zoology. Though he had views that were then in opposition to popular opinion, it has been said that, "everywhere and foremost a teacher, no educational influence of his time was so great as that exerted by him." The splendid Museum of Comparative Zoology at Cambridge, Massachusetts, is a lasting memorial to the ardor and devotion of Louis Agassiz. A son, who bore his name, did much to perpetuate the aims of this institution, besides being a distinguished investigator on his own account. A few years after his arrival in America, his wife having died, Professor Agassiz married Elizabeth Cabot Carey, a writer and teacher. She accompanied the Agassiz expedition to Brazil in 1865, and was also a member of the Hasler deep-sea dredging expedition in 1871-1872. The last enterprise fathered by Agassiz was the summer school of natural history that he established on the coast of Massachusetts a few months before his death, at the age of sixty-six. His resting-place in Mount Auburn Cemetery, Cambridge, is marked by a boulder from the Swiss glacier of the Aar where he pursued his first studies in glacial science, and the pine trees about it were taken from Swiss soil. Thus, writes Mrs. Agassiz, "the land of his birth and the land of his adoption are united in his grave." [Illustration: FROM THE ROUSE CRAYON PORTRAIT MADE IN 1834. NOW IN THE CONCORD PUBLIC LIBRARY HENRY DAVID THOREAU FROM THE WALDEN EDITION OF THOREAU'S WRITINGS. BY COURTESY OF HOUGHTON MIFFLIN COMPANY] _AMERICAN NATURALISTS_ _Henry David Thoreau_ THREE