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THE POPULAR SCIENCE MONTHLY.

dences of glacial action, in erratic blocks, polished and striated rock-surfaces, and terminal moraines. Naturally this served to confirm him in his belief in the universality of the ice-period; and, upon his departure for Brazil, in 1865, he announced his confident expectation of finding records of the former existence of glaciers in that country; for, according to his belief, not only most of the Northern, but also most of the Southern Hemisphere was, during the glacial epoch, encased in ice. The evidences of glacial action in the United States are fully discussed by Agassiz in his "Lake Superior," a work on the physical character, vegetation, and animals, of Lake Superior, compared with those of other and similar regions.

Agassiz was a firm believer in the diversity of origin of the human race, and his views on this point are ably presented in the Christian Examiner for July, 1850, and in an introduction to Nott and Gliddon's "Types of Mankind." While denying the unity of origin of the races of mankind, he by no means denies their essential unity as one brotherhood. He regards all races of men as possessing in common the moral and intellectual attributes of humanity which raise them above the brutes. But intellectual relationship does not imply community of origin. The geographical distribution of animals shows that distinct zoological provinces are each characterized by peculiar fauna, and that therefore animals did not originate from a common centre nor from a single pair. The races of men, in their natural distribution, cover the same ground as the zoological provinces, and he believes there is every reason to suppose that these races originally appeared as nations in the regions they now occupy. That the differences at present observed between various races are primitive, and have not been the result of modification from one common ancestral type, he believed is evidenced by the monuments of Egypt, which show that, for 5,000 years, there has been no physical change in the negro and Caucasian.

In 1850 there appeared in the Transactions of the American Academy of Arts and Sciences an article on the naked-eyed Medusæ, being Part I. of Agassiz's "Contributions to the Natural History of the Acalephæ of North America." He includes all the naked-eyed Medusæ in one family, and shows that the number of tentacles and the position of the ovaries alone cannot be considered as family characters. The true characters consist in a gelatinous disk, with a reentering margin, along which passes a submarginal tube connecting with the circulatory tubes proceeding from a central digestive cavity. Upon the margin are the tentacles and eye-specks. The reproductive organs are situated along the circulatory tubes. The generation is alternate, one form being polyp-like, the other medusoid. The nervous cord follows the circular submarginal tube, and consists of several rows of nucleated cells, alternating one with another. It passes into the bulbs at the base of the marginal tentacles, in which are situated the eye-specks. A branch of nerve-thread passes also along each of the