* 
Review of Darwin's Theory on the Origin of Species. 155 
the two, and, indeed, is necessary to our purpose; for this con- 
trast brings out most prominently, and sets in strongest light 
shade the main features of the theory of the origination of 
is by no means absolute: all species vary more or less, and some 
vary remarkably—partly from the influence of altered eircum- 
stanees, and partly (and more really) from unknown constitu- 
us 
dividuals are mingled i | 
general sterility of hybrid progeny, interposes an effectual bar- 
ner against the blending of the original species by crossing. 
‘rom this generally accepted view the well-known theory of 
Serna and the recent one of Darwin diverge in exactly oppo- 
> Girections, i 
That of Agassiz differs fandamentally from the ordinary view 
only in this, that it discards the idea of a common descent as 
the real of union among the individuals of a species, anc 
also the idea of a local origin,—supposing, instead, that each 
Species originated simultaneously, generally speaking over the 
whole geographi 
area it now occupies or has oceupied, and 
Pty ae tot sunt, quot di formas ab initio produxit Infinitum Ens; que 
“, secundum generationis inditas leges, produxere plures, at sibi semper similes. ce 
ve 
—Linn, Phil, Bot., 99, 15 
