28 ORTHOGENETIC EVOLUTION IN PIGEONS. 



The direction is as certain as that the adult male stands in advance of the adult 

 female, and still more in advance of the young bird. The significance of the case 

 lies mainly in the fact that it is not an isolated or exceptional one. Many other 

 species tell more or less perfectly the same story. 



A parallel case, only carried still farther in the same direction, is found in the 

 mourning-dove (Zenaidura carolinensis) . The adult male and female differ but 

 slightly, each having only about a dozen chequers visible on each side. These are 

 confined to the scapulars and to a few feathers at the posterior upper edge of the 

 wing. In the young they are more numerous (pi. 7, fig. A), but less so than in the 

 young passenger-pigeon. The middle and fore parts of the wing in the adult have 

 no visible chequers, but a few concealed ones which may be seen on lifting the 

 overlying feathers. These concealed chequers, and other differences between old 

 and young, show that the species has its origin in a chequered stock, and that its 

 history has been analogous to that of the passenger-pigeon. 



The white-faced pigeon (Melopelia leucoptera) is a most instructive form. 

 Although much more highly accomplished than the mourning-dove in the arts of 

 display of form, feathers, and voice, it has suffered a complete effacement of the 

 chequers it once possessed in common with other members of the family (see text- 

 figs. 8 and 14). Indubitable proof of this is to be seen in the Juvenal feathers, which 

 in some cases exhibit a few pale vestigial spots in the last two rows of long coverts, 

 at points where the chequers are usually best developed in chequered species. 

 Another striking proof is to be found in the coverts and scapulars of the adult 

 bird, where we find, on lifting the feathers, distinctly outlined areas, corresponding 

 in shape and position with reduced chequers, but from which the black pigment 

 has disappeared. These vestigial outlines, structurally defined, were first noticed 

 in a female bird of a dark shade. 10 The outlines were more perfect than in lighter 

 birds obtained from Arizona and California. 



10 Captured in Jamaica by Dr. Humphreys. 



EXPLANATION OK PLATE 7. 



A. Wing of Juvenal mourning-dove, Zenaidura carolinensis; age 4 weeks. Natural size. Hayashi 



del., June 1897. 



Left wing in first plumage. The tertials have 2 black spots, the dorsal one having no sharp bounding-line. The 

 darker spots are at the upper part of the posterior bar. The next bar has 8 spots, and next 8. 



Most of the scapulars have two spots, and many of the anterior lesser coverts bear indistinct spots. Spots grow 

 darker backward. These spots are strikingly like those of the young Ectopistes. 



Feathers edged with a dull buff-color. The quills are much like those of Ectopistes, but the edging is not of so 

 rich and deep a color. 



B. Wing of juvenal bronze-wing, female, Phaps chalcopiera. Natural size. Hayashi del., Dec. 1905. 

 Left wing at four weeks. 



(1) Oblique streak which has about 10 feathers in one or two rows. These lie just in front of the fourth row in 

 wing-coverts, counting from behind. The feathers of the streak have each one black spot on lower web, only slightly 

 iridescent, and they are already long enough to reach over the tips of some feathers of the fourth row. 



(2) On the tertials it can be seen plainly how the spots arise in or from the dark center of the turtle-dove pattern, 

 a pale transverse band, running from the pale edge of the feather inward for all lengths, from a part of a millimeter 

 to one-half or two-thirds of the width of the outer web. The cross-band is of same color as edge of feather. It means 

 that pigment fails to appear here, and, as if in compensation, more pigment is laid down in front of the band, thus 

 producing the spot or element of the bar; and this spot in adult feathers is built much more strongly more black 

 pigment and strong iridescence. 



In another specimen of about the same age, also a female, I measured these cross-bands and found them to be 

 from 2 to 3 mm. in width and 1 to 8 mm. in length. They stand 15 mm. distant from the tip of the feather. In the 

 specimen drawn I see these bands in the row of long coverts, but not so well defined. Evidently these cross-bands 

 or bars have had much to do in shaping spots and in giving eye-like borders (diamond-dove, adult bronze-wing, etc.). 



The wing drawn was injured a little at outer edge. 



