CUVIER’S DEFINITION OF SPECIES. 51 
from one another, or from common ancestors, or which are 
as similar to these as the latter are among themselves.” 
In dealing with this matter, Cuvier reasoned in the 
following manner :—“ In those organic individuals, of which 
we know that they are descended from one and the same 
common form of ancestors—in which, therefore, their com- 
mon ancestry is empirically proved—there can be no doubt 
that they belong to one species, whether they differ much or 
little from one another, or whether they are almost alike or 
very unlike. Moreover, all those individuals also belong to 
this species which differ no more from the latter (those 
proved to be derived from a common stock) than these differ 
from one another.” In a closer examination of this definition 
of species given by Cuvier, it becomes at once evident that 
it is neither theoretically satisfactory nor practically appli- 
eable. Cuvier, with this definition, began to move in the 
same circle in which almost all subsequent definitions 
of species have moved, through the assumption of their 
immutability. 
Considering the extraordinary authority which George 
Cuvier has gained in the science of organic nature, and in con- 
sequence of the almost unlimited supremacy which his views 
exercised in zoology, during the first half of our century, it 
seems appropriate here to examine his influence a little more 
closely. This is all the more necessary as we have to com- 
bat, im Cuvier, the most formidable opponent to the Theory 
of Descent and the monistic conception of nature. 
One of the many and great merits of Cuvier is that he 
stands forth as the founder of Comparative Anatomy. While 
Linnzeus established the distinction of species, genera, orders, 
and classes mostly upon external characters, and upon sepa- 
