134 PROCEEDINGS OF THE AMERICAN ACADEMY 



homogeneous in its organic productions and modified by 

 climatic changes, but as a primitive adaptation of organic 

 types to similar corresponding physical features, which have 

 remained respectively unchanged since the first introduction 

 upon earth of these organisms. Admitting with Dr. Gray 

 the immensely long duration of even the present period, he 

 did not think that the regular order and organic connection 

 which everywhere exist between the different types of ani- 

 mals and plants upon the whole surface of our globe, could 

 have been established by physical changes, or even essentially 

 modified by them. With reference to the single origin of 

 conspecific individuals, he thought that the warfare which so 

 many species wage upon others was in itself an insuperable 

 objection to the assumption that any one species could have 

 originated in a single pair. 



The President remarked, that the appearance of the same 

 species on different or opposite parts of the globe admitted of 

 explanation by supposing that originally a zone, or isothermal 

 belt, which existed in each climate, contained all the species 

 capable of flourishing in that climate so long as the climate 

 remained stationary; and that in the lapse of ages a great 

 portion of these plants had disappeared or died out, under the 

 casualties to which plants are liable, some having disappeared 

 altogether, and others remaining only in localities, defined by 

 longitudes, in different parts of the same zone ; so that at 

 the present day, while the general character of the vegetation 

 is different in different hemispheres and countries, still a suffi- 

 cient number of species might be extant in, and common to, 

 both hemispheres, to represent a part of the original growth. 

 This explanation appeared to him more probable than the 

 supposition that these plants had more recently migrated 

 from any one country to its antipodes, passing over the inter- 

 mediate regions. 



Professor Gray rejoined, that his views would in a good 

 degree harmonize with those of the President, with the im- 

 portant exception that he regarded any former more homo- 



