Neither was his summer work necessarily suspended during winter, his Cambridge and Nahant homes being only about fifteen miles distant from each other. He writes to his friends, the Holbrooks, at this time, "You can hardly imagine what a delightful place Nahant is for me now. I can trace the growth of my little marine animals all the year round without interruption, by going occasionally over there during the winter. I have at this moment young medusae budding from their polyp nurses, which I expect to see freeing themselves in a few weeks." In later years, when his investigations on the medusae were concluded, so far as any teaching from the open book of Nature can be said to be concluded, he pursued here, during a number of years, investigations upon the sharks and skates. For this work, which should have made one of the series of "Contributions," he left much material, unhappily not ready for publication. In August, 1857, Agassiz received the following letter from M. Rouland, Minister of Public Instruction in France. TO PROFESSOR AGASSIZ. PARIS, August 19, 1857. SIR, By the decease of M. d'Orbigny the chair of paleontology in the Museum of Natural History in Paris becomes vacant. You are French; you have enriched your native country by your eminent works and laborious researches. You are a corresponding member of the Institute. The emperor would gladly recall to France a savant so distinguished. In his name I offer you the vacant chair, and should congratulate your country on the return of a son who has shown himself capable of such devotion to science. Accept the assurance of my highest esteem, ROULAND. Had it been told to Agassiz when he left Europe that in ten years he should be recalled to fill one of the coveted places at the Jardin des Plantes, the great centre of scientific life and influence in France, he would hardly have believed himself capable of refusing it. Nor does a man reject what would once have seemed to him a great boon without a certain regret. Such momentary regret he felt perhaps, but not an instant of doubt. His answer expressed his gratitude and his pleasure in finding himself so remembered in Europe. He pleaded his work in America as his excuse for declining a position which he nevertheless considered the most brilliant that could be offered to a naturalist. In conclusion he adds: "Permit me to correct an error concerning myself. I am not French, although of French origin. My family has been Swiss for centuries, and spite of my ten years' exile I am Swiss still."