SPECIFIC STABILITY. 133 



In a bird which has been kept and studied like the pigeon, 

 it is difficult to believe that any remarkable spontaneous 

 variations would pass unnoticed by breeders,- or that they 

 would fail to be attended to and developed by some one 

 fancier or other. On the hypothesis of indefinite variability, 

 it is then hard to say why pigeons with bills like toucans, 

 or with certain feathers lengthened like those of trogans, 

 or those of birds of paradise, have never been produced. 

 This, however, is a question which may be settled by ex- 

 periment. Let a pigeon be bred with a bill like a toucan's, 

 and with the two middle tail-feathers lengthened like those 

 of the king bird of paradise, or even let individuals be 

 produced which exhibit any marked tendency of the kind, 

 and the claim to indefinite variability shall be at once 

 conceded. 



As yet all the changes which have taken place in pigeons 

 are of a few definite kinds only, such as may be well con- 

 ceived to be compatible with a species possessed of a 

 certain inherent capacity for considerable yet definite 

 variation, a capacity for the ready production of certain 

 degrees of abnormality which once attained cannot be 

 further increased. 



Mr. Darwin himself has already acquiesced in the pro- 

 position here maintained, inasmuch as he distinctly affirms 

 the existence of a marked internal barrier to change in 

 certain cases. And if this is admitted in one case, the 

 principle 1 is conceded, and it immediately becomes pro- 



1 Mr. Darwin, in his "Descent of Man," just published, distinctly 

 admits the existence of such internal powers. Thus, in vol. i. p. 154, he 

 says, of the exciting causes of modification, "they relate much more 

 closely to the constitution of the varying organism, than to the nature of 

 the 'conditions to which it has been subjected." In a note on page 223 he 

 speaks of "incidental results of certain unknown differences in the con- 



