186 



ORTHOGENETIC EVOLUTION IN PIGEONS. 



Nature meets our need much better in some wild species, in which the apical 

 mark has been well-preserved in the immature feathers. The ground-doves of the 

 genus Geopelia amplify the test to multiple demonstrations, in one and the same 

 plumage. 



Let us examine three successive stages in the wing of the young peaceful ground- 

 dove (Geopelia tranquilla). At the age of 17 days (text-fig. 31) the earlier feathers 

 (shown in text-fig. 30) are already well-developed and the oblique tract is only par- 

 tially feathered. Excluding for the moment the scapulars, primaries, secondaries, 

 and tertials, we see three conspicuous rows of coverts (i to in) ; then a fourth row 





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TEXT-FIGURE 30. 

 Ju venal Geopelia Iranguilla (Gtl-Bl), age 10 days. Hatched July 14, 1899. Hayashi del., July 24, 1899. x 2. 



The scapulars number 14 or 15 in about two rows. The fourth row of coverts are conspicuously downy in ap- 

 pearance, but form a distinct row with whitish-yellow tips. The barbs are loose, spreading wide apart. These are 

 represented roughly in lines across the light tips. The feathers in the third row are also somewhat of the same 

 character, but yet more compact and regular, as are the posterior rows. In front of the fourth row there are 

 shorter feathers, more thickly set, with light tips, but dark elsewhere. There are 6 or 7 rows of these feathers. 

 The elbow is bare. The fourth row runs along the forearm bone, but between it and the anterior feathers will soon 

 :ippe;ir one or two rows of feathers that have a tip of less than one-half the width of the earlier feathers, and these 

 will prow over and completely cover the fourth row before these latter feathers fall out. Indeed, some feathers with 

 bluck tips will appear behind these later feathers before the fourth row is lost. 



(iv) covered to near the tips by the feathers of the oblique tract; and in front of 

 this tract, 15 lesser coverts. The apical mark is 1.5 mm. wide in the lesser coverts, 

 and from 1.5 mm. to 2 mm. in the three posterior rows. 



In the oblique tract we see 13 feathers arranged rather obscurely, in from 2 to 

 3 unevenly developed rows (1, 2, 3). Five of these feathers, of which 2 are only 

 pins, have no pale apical marks, but instead, narrow black tips, differing from the 

 black crescents of the adult only in their lesser width and depth of color. These 

 tire the most belated feathers of the tract that are visible at this age. Between the 

 innermost half-expanded, black-tipped feather and the black-tipped pin below are 

 seen 6 feathers, in which the pale apical mark is present, but reduced to about one- 

 third its width in the lesser coverts. In line with these 6 feathers, near the bend of 

 the wing, is a single feather (1 6) with the apical mark reduced to about one-half 

 width; while just in front of the lower two of these feathers, and second in front of 





