616 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 depart- 

 ure for Brazil, in 1865, he announced his confident expectation of find- 

 ing 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 brother- 

 hood. 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 Acad- 

 emy of Arts and Sciences an article on the naked-eyed Medusae, being 

 Part I. of Agassiz's " Contributions to the Natural History of the 

 Acalephse of North America." He includes all the naked-eyed Me- 

 dusas in one family, and shows that the number of tentacles and the 

 position of the ovaries alone cannot be considered as family char- 

 acters. The true characters consist in a gelatinous disk, with a re- 

 entering 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 tbe base of the marginal tentacles, in which are situated the 

 eye-specks. A branch of nerve-thread passes also along each of the 



