35© THE STORY OF A BIRD LOVER 



forms is allowed, as, for instance, domesticated 

 pigeons, the reversion to the common ancestral 

 type is rapid and eventually complete. 



Birds so widely separated in appearance as fan- 

 tails and carrier pigeons breed readily together, 

 and their offspring are fertile ; and, on the other 

 hand, birds so closely resembling one another as 

 the hermit and the olive-backed thrush of eastern 

 North America, which at points have the same 

 breeding-range, appear never to interbreed, or, 

 if such an event occurs, the offspring — the 

 hybrids — do not perpetuate the new form so 

 originated. All the foregoing is set forth in 

 some detail in order to maintain the position that, 

 while the efforts of man have produced wide di- 

 vergences in thoroughbred forms of domesticated 

 animals — types that any naturalist would consider 

 as separate species if they were wild — they are 

 only to be regarded as morphological species, and 

 have no true physiological basis. The converse 

 seems to be the rule among wild animals. 



I am thoroughly of the opinion that a careful 

 and prolonged effort, conducted under the proper 

 conditions and with proper equipment, would re- 

 sult not only in the establishment of what I have 

 termed morphological species, but that ultimately 

 in a laboratory of the kind I have indicated, true, 

 physiological species could be established ; forms 

 that would not revert to an ancestral type if left 



