178 PROCEEDINGS OF THE AMERICAN ACADEMY 



be ascribed to the influence of climate. In passing from the 

 arctic to the tropical regions, the uniformity of animal life in the 

 former passes gradually into the extreme diversity of that in the 

 latter, and in the causes of difference in the tropics Professor 

 Agassiz said he saw the reasons for all differences, wherever 

 observed. How far back, he asked, does this state of things 

 go ? In the tertiary times of Australia the peculiar types of 

 animal life existed which give at the present time the distinc- 

 tive character to its Fauna, and the same is true of the ter- 

 tiary Fauna of South America. These facts, and others like 

 them, have led him to believe that animals were primarily 

 distributed over the surface according to a plan hardly intel- 

 ligible as yet to us, but independent of climatic influences. 

 This plan he believed included the preparation for the earth's 

 surface and the various external conditions of their existence 

 for its inhabitants, before they were created, very much as a 

 householder lays his foundation and builds the superstructure 

 and arranges the furniture of the interior for his residence be- 

 fore occupying it. 



Professor Gray had quoted a number of plants as identical 

 in the tertiary and the present period. Des Hayes and Lyell 

 had admitted the same with regard to the animals of these 

 periods. Professor Agassiz said he had doubted the fact in 

 the case of animals, and had therefore early in his scientific 

 career collected many specimens to settle the question, and 

 in every instance where he had sufficient materials he had 

 found that the species of the two epochs supposed to be 

 identical by Des Hayes and Lyell were in reality distinct, 

 although closely allied species. He was therefore inclined to 

 ask whether it might not be possible that the same is the case 

 with the plants of the tertiary period and those of the present 

 day ? He could not but believe that, if Professor Gray were 

 to exercise the same critical judgment upon the fossil Flora 

 which he does with reference to the existing Flora, he would 

 find differences between the species of the two epochs simi- 

 lar to those found in the animal world. There is not, at the 



