CHAPTER III. 



THE PROBLEM OF THE ORIGIN OF SPECIES (CONTINUED). 1 



In the Australian crested pigeon (Ocyphaps lophotes) we find the homologues 

 of the two bars of the rock-pigeon, the elemental spots having nearly the same form, 

 but a much more brilliant color (pi. 8). Moreover, in front of the secondaries and 

 the long coverts which bear these two bars, each row of the median and lesser 

 coverts of the wing bears a narrow band of black (text-fig. 11), and these, nine to 

 ten in number, gradually diminish in width until at the anterior end they become 

 mere lines. 



Between these bands and the two posterior bars there is the sharpest contrast 

 in form as well as in color, the one being plain black and the other iridescent green 

 and purple. Nevertheless, it can be shown that the two marks are serial homo- 

 logues, two different forms, but one derived from the other. From the form and 

 position of the bars, from the close resemblance they hold with the bars of the rock- 

 pigeon, which resemblance is still closer in the juvenal feathers (pi. 8, fig. B, and 

 text-fig. 10), and from the fact that bars among pigeons appear everywhere to be 

 made up of like constituent elements, I feel certain of these homologues. 



The longitudinal spots composing the bars are, then, safely identified with the 

 so-called chequers in the wild rock-pigeon and its domestic descendants, and both 

 have been derived from the same old mark, named the dark center, of the turtle- 

 dove pattern. 



There can be no doubt, therefore, as to which of the two marks found in the 

 wing of the crested pigeon is the older element, and this relation furnishes the key 

 to further orientation. The transformation of the longitudinal spots into the later 

 transverse bands has already swept over a large portion of the field. Has the change 

 been gradual and slow, or was it all accomplished suddenly, and in such a manner 

 that no genetic continuity ever existed between the two marks? Were no inter- 

 mediate steps or transitional phases required to pass from one extreme to the other? 

 Was there no connection between them, and did one succeed the other as one 

 picture replaces another by a turn of the kaleidoscope? Was there no predetermined 

 direction of change manifest at any time before fulfilment? If orderless and 

 directionless, then its appearance in the anterior rather than the posterior part 

 of the wing, and its complete regularity in this part of the field, have no particular 

 significance. 



These questions answer themselves in a most decisive way in the present case. 

 We shall see that the change is a progressive one, still moving on in a definite 

 course, which is premarked by gradual transitional phases. If these bands and 

 bars were not found in one and the same bird, but one in one bird, the other in 

 another, no one could hesitate to pronounce them distinct specific characters, and 

 the mutationist would undoubtedly claim at least one saltation between them. 

 But nature has here put these characters in such relations, joined them by such 

 indubitable connecting stages, and now repeats her steps in such gradual ways 



1 This was written in 1905 as a continuation of the preceding address (Chapter II). It is here published for the 



first time. — Ed. 



37 



