other saurians, and really higher than the turtles? Innumerable questions of this kind, of great importance for zoology, are suggested at every step, as soon as we compare the present distribution of animals with that of the inhabitants of former geological periods. Among crustacea, it is very remarkable that trilobites and limulus-like forms are the only representatives of the class during the paleozoic ages; that macrourans prevailed in the same manner during the secondary period; and that brachyurans make their appearance only in the tertiary period. Do you discover in your results any connection between such facts and the present distribution of crustacea? There is certainly one feature in their classification which must appear very striking,--that, taken on a large scale, the organic rank of these animals agrees in the main with their order of succession in geological times; and this fact is of no small importance when it is found that the same correspondence between rank and succession obtains through all classes of the animal kingdom, and that similar features are displayed in the embryonic growth of all types so far as now known. But I feel my head is growing dull, and I will stop here. Let me conclude by congratulating you on having completed your great work on crustacea. . . Agassiz returned to the North in the spring of 1853 by way of the Mississippi, stopping to lecture at Mobile, New Orleans, and St. Louis. On leaving Charleston he proffered his resignation with deep regret, for, beside the close personal ties he had formed, he was attached to the place, the people, and to his work there. He had hoped to establish a permanent station for sustained observations in South Carolina, and thus to carry on a series of researches which, taken in connection with his studies on the New England coast and its vicinity, and on the Florida reefs and shores, would afford a wide field of comparison. This was not to be, however. The Medical College refused, indeed, to accept his resignation, granting him, at the same time, a year of absence. But it soon became evident that his health was seriously shaken, and that he needed the tonic of the northern winter. He was, indeed, never afterward as strong as he had been before this illness.