of the European Ornis, and its Causes. 301 



ous requirements. The principle of the separation of species is 

 in all cases essentially the same ; in respect of its practical ap- 

 plication, we can only hold different views as to the degree of 

 requirement, and this diversity is purely subjective. 



The abrupt gap between the two schools is considerably en- 

 larged, if we differ also in the principle and not merely in the 

 degree of requirement. The dominant zoology universally assumes 

 that different species must be actually different in their pro- 

 perties — that is to say, separated by well-defined limits in their 

 characters. This, however, is not theoretically the view of the 

 freer unbridled ornithology. In this it stands as a theoretical 

 principle that nature everywhere presents transitions between 

 species, as between subspecies. With this therefore every kind 

 of objective conception falls to the ground. The only means of 

 comprehension that remains consists in the comparison of in- 

 dividuals lying before the observer. The ornithology which pro- 

 ceeds on the principle of allowing universal transition, and sets 

 lax requirements on the species, runs the danger of becoming 

 incapable of being checked by others, and thereby necessarily 

 renouncing all further influence in favour of a deviation. It is 

 throughout of a subjective nature, and therefore not com- 

 municable. 



From this it follows, in my opinion, that it must remain with- 

 out results, as, indeed, it has hitherto done, to dispute as to the 

 boundaries of species in the two distinct ornithological schools. 

 All that can be done towards an elucidation is to indicate the 

 irreconcileable degree of the diversity in the two tendencies and 

 to establish a synonymy for both views. 



Both the digressing sects do well when they avoid all disputes ; 

 when they at the utmost confine themselves to ascertaining what 

 objective matter of fact runs parallel to the two different sub- 

 jective views. This is the only question on which unity can be 

 attained on both sides, although not to the satisfaction of both 

 parties. 



All that the ornithologists with more rigid requirements can 

 do in this direction for the advancement of their science is that 

 they should come to an understanding among themselves as to 

 the way in which the so-called local races, about fifty in number, 



