microscope, handled by him like a master. Tiedemann's lectures were very learned, and Agassiz always spoke of his old teacher in comparative anatomy and physiology with affectionate respect and admiration. He was not, however, an inspiring teacher, and though an excellent friend to the students, they had no such intimate personal relations with him as with Leuckart and Bischoff. From Bronn, the paleontologist, they received an immense amount of special information, but his instruction was minute in details rather than suggestive in ideas; and they were glad when their professor, finding that the course must be shortened for want of time, displayed to them his magnificent collection of fossils, and with the help of the specimens, developed his subject in a more general and practical way.* (* This collection was purchased in 1859 by the Museum of Comparative Zoology in Cambridge, Massachusetts, and Agassiz had thus the pleasure of teaching his American pupils from the very collection in which he had himself made his first important paleontological studies.) Of the medical professors, Nageli was the more interesting, though the reputation of Chelius brought him a larger audience. If there was however any lack of stimulus in the lecture rooms, the young friends made good the deficiency by their own indefatigable and intelligent study of nature, seeking to satisfy their craving for knowledge by every means within their reach.* (* The material for this account of the student life of the two friends at Heidelberg and of their teachers was chiefly furnished by Alexander Braun himself at the close of his own life, after the death of Agassiz. The later sketches of the Professors at Munich in 1832 were drawn in great part from the same source.)

As the distance and expense made it impossible for Agassiz to spend his vacations with his family in Switzerland, it soon became the habit for him to pass the holidays with his new friend at Carlsruhe. For a young man of his tastes and acquirements a more charming home-life than the one to which he was here introduced can hardly be imagined. The whole atmosphere was in harmony with the pursuits of the students. The house was simple in its appointments, but rich in books, music, and in all things stimulating to the thought and imagination. It stood near one of the city gates which opened into an extensive oak forest, in itself an admirable collecting ground for the naturalist. At the back certain rooms, sheltered by the spacious garden from the noise of the street, were devoted to science. In the first of these rooms the father's rich collection of minerals was arranged, and beyond this were the laboratories of his sons and their friends, where specimens of all sorts, dried and living plants, microscopes and books of reference, covered the working tables. Here they brought their treasures; here they drew, studied, dissected, arranged their specimens; here they discussed the theories, with which their young brains were teeming, about the growth, structure, and relations of animals and plants.* (* See "Biographical Memoir of Louis Agassiz" by Arnold Guyuot, in the "Proceedings of U.S. National Academy".)

From this house, which became a second home to Agassiz, he wrote to his father in the Christmas holidays of 1826:. . ."My happiness would be perfect were it not for the painful thought which pursues me everywhere, that I live on your privations; yet it is impossible for me to diminish my expenses farther. You would lift a great weight from my heart if you could relieve yourself of this burden by an arrangement with my uncle at Neuchatel. I am confident that when I have finished my studies I could easily make enough to repay him. At all events, I know that you cannot pay the whole at once, and therefore in telling me frankly what are our resources for this object you would do me the greatest favor. Until I know that, I cannot be at peace. Otherwise, I am well, going on as usual, always working as hard as I can, and I believe all the professors whose lectures I attend are satisfied with me.". . .His father was also pleased with his conduct and with his progress, for about this time he writes to a friend, "We have the best possible news of Louis. Courageous, industrious, and discreet, he pursues honorably and vigorously his aim, namely, the degree of Doctor of Medicine and Surgery."

In the spring of 1827 Agassiz fell ill of a typhus fever prevalent at the university as an epidemic. His life was in danger for many days. As soon as he could be moved, Braun took him to Carlsruhe, where his convalescence was carefully watched over by his friend's mother. Being still delicate he was advised to recruit in his native air, and he returned to Orbe, accompanied by Braun, who did not leave him till he had placed him in safety with his parents. The following extracts from the correspondence between himself and Braun give some account of this interval spent at home.

AGASSIZ TO BRAUN.

ORBE, May 26, 1827.

. . .Since I have been here, I have walked faithfully and have collected a good number of plants which are not yet dry. I have more than one hundred kinds, about twenty specimens of each. As soon as they can be taken out of the press, I'll send you a few specimens of each kind with a number attached so that you may identify them. Take care that you do not displace the numbers in opening the package. Should you want more of any particular kind let me know; also whether Schimper wishes for any. . .At Neuchatel I had the good fortune to find at least thirty specimens of Bombinator obstetricans with the eggs. Tell Dr. Leuckart that I will bring him some,--and some for you also. I kept several alive laid in damp moss; after fourteen days the eggs were almost as large as peas, and the little tadpoles moved about inside in all directions. The mother stripped the eggs from her legs, and one of the little tadpoles came out, but died for want of water. Then I placed the whole mass of eggs in a vessel filled with water, and behold! in about an hour some twenty young ones were swimming freely about. I shall spare no pains to raise them, and I hope, if I begin aright, to make fine toads of them in the end. My oldest sister is busy every day in making drawings for me to illustrate their gradual development. . .I dissect now as much and on as great a variety of subjects as possible. This makes my principal occupation. I am often busy too with Oken. His "Natur-philosophie" gives me the greatest pleasure. I long for my box, being in need of my books, which, no doubt, you have sent. Meantime, I am reading something of Universal History, and am not idle, as you see. But I miss the evenings with you and Schimper at Heidelberg, and wish I were with you once more. I am afraid when that happy time does come, it will be only too short. . .

BRAUN TO AGASSIZ.

HEIDELBERG, May, 1827.

. . .On Thursday evening, the 10th, I reached Heidelberg. The medical lectures did not begin till the second week of May, so that I have missed little, and almost regret having returned so soon. . . I passed the last afternoon in Basel very pleasantly with Herr Roepper, to whom I must soon write. He gave me a variety of specimens, showed me many beautiful things, and told me much that was instructive. He is a genuine and excellent botanist, and no mere collector like the majority. Neither is he purely an observer like Dr. Bischoff, but a man who thinks. . .Dr. Leuckart is in raptures about the eggs of the "Hebammen Krote," and will raise them. . .Schweiz takes your place in our erudite evening meetings. I have been lecturing lately on the metamorphosis of plants, and Schimper has propounded an entirely new and very interesting theory, which will, no doubt, find favor with you hereafter, about the significance of the circular and longitudinal fibres in organisms. Schimper is fruitful as ever in poetical and philosophical ideas, and has just now ventured upon a natural history of the mind. We have introduced mathematics also, and he has advanced a new hypothesis about comets and their long tails. . . Our chief botanical occupation this summer is the careful observation of all our plants, even the commonest, and the explanation of whatever is unusual or enigmatical in their structure. We have already cracked several such nuts, but many remain to be opened. All such puzzling specimens are spread on single sheets and set aside. . .But more of this when we are together again. . .Dr. Leuckart begs you to study carefully the "Hebammen Unke;"* (* Bombinator obstetricans referred to in a former letter.) to notice whether the eggs are already fecundated when they are in the earth, or whether they copulate later in the water, or whether the young are hatched on land, and what is their tadpole condition, etc. All this is still unknown. . .

AGASSIZ TO BRAUN.

ORBE, June 10, 1827.

. . .Last week I made a very pleasant excursion. You will remember that I have often spoken to you of Pastor Mellet at Vallorbe, who is much interested in the study of the six-legged insects. He invited me to go to Vallorbe with him for some days, and I passed a week there, spending my time most agreeably. We went daily on a search after insects; the booty was especially rich in beetles and butterflies. . .I examined also M. Mellet's own most excellent collection of beetles and butterflies very carefully. He has many beautiful things, but almost exclusively Swiss or French, with a few from Brazil,--in all about 3,000 species. He gave me several, and promises more in the autumn. . .He knows his beetles thoroughly, and observes their habits, haunts, and changes (as far as he can) admirably well. It is a pity though that while his knowledge of species is so accurate, he knows nothing of distribution, classification, or general relations. I tried to convince him that he ought to collect snails, slugs, and other objects of natural history, in the hope that he might gain thereby a wider insight. But he would not listen to it; he said he had enough to do with his Vermine.

My brother writes me that my box has arrived in Neuchatel. As I am going there soon I will take it then. I rejoice in the thought of being in Neuchatel, partly on account of my brother, Arnold (Guyot), and other friends, and partly that I may study the fishes of our Swiss lakes. The species Cyprinus and Corregonus with their allies, including Salmo, are, as you know, especially difficult. I will preserve some small specimens in alcohol, and, if possible, dissect one of each, in order to satisfy myself as to their identity or specific variety. As the same kinds have received different names in different lakes, and since even differences of age have led to distinct designations, I will note all this down carefully. When I have made it clear to myself, I will send you a catalogue of the kinds we possess, specifying at the same time the lakes in which they occur. As I am on the chapter of fishes, I will ask you:

1. What are the gill arches? 2. What the gill blades? 3. What is the bladder in fishes? 4. What is the cloaca in the egg-laying animals? 5. What signify the many fins of fishes? 6. What is the sac which surrounds the eggs in Bombinator obstetricans?

. . .Tell Dr. Leuckart I have already put aside for him the