THE PROBLEM OF THE ORIGIN OF SPECIES. 



23 



This ancestral mark is a dark spot filling the whole central part of the feather, 

 leaving only a narrow distal edge of a lighter color. This mark is still well preserved 

 in some of the old-world turtle-doves — best in the Oriental turtle-dove of China and 

 Japan. The chequer of Columba livia differs from the dark center of Turtur orien- 

 talis (text-fig. 3) only in form and in having a lateral position. Typically this spot 

 appears in pairs, one on each side of the feather. The two spots represent the two 

 halves of the old central spot, which becomes more or less deeply divided by the 

 disappearance of pigment along the shaft of the feather. This change begins at 

 the tip of the feather and advances inward, but usually more rapidly along the 

 shaft than at the sides, thus resulting in two chequers with more or less pointed 

 tips. The direction of change again coincides with that of embryonic develop- 

 ment — the tips of the feather, where it begins, being first in order of development. 

 In many chequered rock-pigeons we may find in the dorsal (inner) feathers of 

 the bars undivided central spots, which pass gradually into the typical chequers 

 as we pass towards the lower (outer) ends of the bars. Transitional stages of 



Explanation of Plate 5 — Continued. 

 B. Male homer, No. 7, hatched May 1, 1904. X 0.8. Hayashi del., Oct. 1904. 



The male bearing this wing resembles his sire in size and general form. The chequers on the scapulars are 

 stronger and more numerous than in the sire, but fall far below the dam. The third bar has about the same number 

 of spots, but these are here a little stronger. 



The second bar inclines to red (red = light shading; black or rather dark gray = black). The shaft-line and the 

 lower edge are also reddish gray in three or four of the upper (inner) tertials and long coverts. 



Measurements. 



The eighth to fourteenth secondaries of the first bar have spots almost too indistinct to measure with certainty. 

 (See preceding figure.) 



1904. 



The quills are whitish, but 



C. Female homer, No. 8, hatched May 1, 1904. X 0.8. Hayashi del., Oct 



This female is pale, though not quite so pale as homer No. 3 (fig. A, this plate), 

 less so than in homer No. 3. 



Third bar is here scarcely noticeable. 



Second bar begins with 11 mm. width, increasing in second feather to 12 mm. and in third to 13 mm. It runs 

 on nearly evenly to the seventh feather and then becomes gradually thinner. 



First bar has its greatest width on fourth and fifth feathers— 22 and 20 mm. respectively. The tip spot begins 

 on both upper and lower webs of the sixth feather. 



(The details of the breeding history of the three birds shown on this plate arc given in table 7b .if Vol. II. — Ed.) 

 3 



