132 PROCEEDINGS OF THE AMERICAN ACADEMY 



facts, and wished to do so without prejudging the question 

 involved. But he was free to say that the present investiga- 

 tion had confirmed his impression that such terms were prop- 

 erly employed. For although some of these facts would at 

 first seem most readily explicable upon the supposition of the 

 double origin of those species whose present geographical 

 areas are widely dissevered, yet, in his opinion, they would 

 be found, on considering the whole case, far more conforma- 

 ble to the hypothesis of a single local origin for each species 

 at an early time. And in his opinion the actual question 

 now is, — whether each species originated in one local area, 

 whence it has spread, as circumstances permitted, over more 

 or less broad tracts, in some cases becoming discontinuous in 

 area through changes in climate or other physical conditions 

 operating during a long period of time ; or, whether each 

 species originated where it now occurs, probably in as great 

 a number of individuals occupying as large an area, and gen- 

 erally the same area, or even the same discontinuous areas, as 

 at the present time. The latter is understood to be the view 

 of Professor Agassiz. 



To this view Professor Gray objected : — 1. That it offers 

 no scientific explanation of the present distribution of species 

 over the globe ; but simply supersedes explanation, by affirm- 

 ing, that as things now are, so they were at the beginning ; 

 whereas the facts of the case — often very peculiar — ap- 

 pear to demand from science something more than a direct 

 reference of the phenomena as they are to the Divine will. 



2. That the idea of the descent of all similar or conspecific 

 individuals from a common stock is so natural, and so inevita- 

 bly suggested by common observation, that it must needs be 

 first tried upon the problem ; and if the trial be satisfactory, 

 its adoption would follow as a matter of course. 



o. That, since it is conceded that the present era of the 

 Avorld is of extremely long duration, and since it is most 

 probable, not to say certain, that the existing species of 

 plants of the regions in question, or a part of them, are of 



