THE DIVISIBILITY OF CHARACTERS. 



219 



TEXT-FIG UHEjlO. 



Figs. 1-4. Neck-mark of :in adult male Chinese turtle-dove. Spilopeliti r/i/mm-i.v. Natural size. 



del., Dec. 1902. 



Hayashi 



1. Side view of same bird as fig. 5, which shows both sides in one plane. 



Evolution: We have to start with a form most nearly represented in Turtur orientalis of China and Japan. 

 The centers of the wing-feathers there have the black rounded out full behind, leaving only the apical reddish 

 bar, or tip. 



In T. turtwr of Europe, the dark center becomes reduced, ending in an angular point behind. 



In Spiloptilin xiiriili'iiHiii (also bifurcated neck-feathers) the black is still further reduced to a dark mesial 

 stripe. 



In Spil. chinensis even the mesiaj stripe has departed, and the neck-feathers, tipped with white, are bifur- 

 cated. In these two last-named species the neck-feathers are not only bifurcated, but a luri/tr numlicr of roir.i 

 are differentiated. Running back to T. orientalis, we find entire neck-feathers ttJM fewer rows 6 down to only 

 3 or 4. The extension of the number of rows has also been accompanied by an extension of differentiation 

 towards the mid-back of the neck, where the two spots plainly coalesce on the upper three or four rows. 



2. First feather of fifth row (counting downward); right side. This feather comes on the boundary line 

 and has black on the posterior web only; the front web is vinous, like the feathers of the mid-front of the neck 

 and breast and has no bifurcation. The hind half is only touched with white close to the distal end of the black ; 

 elsewhere both webs are vinous-tipped. 



3. FiftR feather of fifth row; left side. This row may be said to form the focal center of differentiation. 

 The feather is widely bifurcated and the tips are white; the basal part up to the last one-fourth is black. 



4. Seventh row; left side. Here the black becomes gray and the white vinous. 



5. Neck-mark (flat) of same bird as figs. 1 to 4. 



This figure shows the continuity of both spots in the mid-back region. We see here how the differentiated 

 feathers pass gradually into vinous or brown, short tips into long tips, and bifurcated into entire. (For the 

 color-scheme of the entire bird, in ink, see pi. 23, vol. I. ED.) 



