1 I i NATURAL HISTOKY OF 



logy itself rests again upon an assumed conclusion. 

 Now, with regard to the second proposition, notwith- 

 standing an unnecessary multiplication of species suc- 

 cessively adopted by other philosophical physiologists, 

 it cannot be denied, that by their hypothesis, many 

 phenomena, most difficult of explanation, are solved in. 

 a -comparatively natural way, and so far deserve more 

 implicit confidence. For the first, scientifically taken, 

 reposes mainly upon the maxim in natural history, 

 which declares, " That the faculty of procreating a 

 fertile offspring, constitutes identity of species, and 

 that all differences of structure and external appear- 

 ance, compatible therewith, are solely the effects re- 

 sulting from variety of climate, food, or accident; 

 consequently, are forms of mere varieties, or of races 

 of one common species /* The second, on the contrary, 

 while admitting the minor distinctions, as the effects of 

 local causes, regards the structural, taken together with 

 the moral and intellectual characters, as indications of 

 a specific nature not referrible to such causes, albeit 

 the species remain prolific by inter-union, which, ac- 

 cording to them, are the source of varieties and inter- 

 mediate races. 



In systematic zoological definitions, the first may be 

 regarded as sufficiently irue, for general purposes of 

 classification ; but, physiologically, it cannot be assumed 

 as positively correct, since there are notable exceptions, 

 most probably in all the classes of the animal kingdom, 



* Buffon and Cnvier have made their definitions some- 

 what more complicated, but essentially the same. 



