52 PHYLOGENY 



The wild passenger pigeon (Ectopistes) bears checkers closely re- 

 sembling those^of the checkered rock pigeon, in form, color, and dis- 

 tribution. In this species the sexes are distinctly differentiated in 

 color; and we have for comparison three stages in an ascending 

 series; namely, the Juvenal, the adult female, and the adult male. As 

 in so many other birds, the male makes the widest departure from 

 original conditions; the female occupies a lower plane; the young 

 are nearly alike in both sexes, and may be said to recapitulate 

 ancestral conditions with less modification than is seen in the adult 

 of either sex. 



In birds taken at random, I count in the left wing and scapulars 

 90 checkers in a Juvenal, 51 in an adult female, and 25 in an adult 

 male. This is pretty conclusive evidence that checkers are, or have 

 been, disappearing in the species. Not only the number, but also the 

 size of the checkers has been reduced. In the female the checkers 

 are for the most part two or more times as large as in the male. The 

 reduction in both respects has been greater in the anterior than in 

 the posterior half of the wing, and greater along the lower edge than 

 in the middle and back regions. 



In this species we may recognize at first sight the homologues of 

 the rock pigeon bars. On the secondaries of the female we find the 

 homologue of the posterior bar, and on the first row of long coverts 

 the homologue of the anterior bar. The latter is scarcely recognizable 

 as a bar; for we see only five or six checkers in the upper half of the 

 row, the lower half being without checkers. Nevertheless, this row 

 represents, so far as it goes, the elements of a bar, which is already 

 too far gone to have even a chance to attain the finish of a perfect bar. 1 



On the secondaries the checkers fall into juxtaposition, forming a 

 continuous bar, with an irregular posterior outline, which indicates 

 that the checkers have been unevenly reduced from behind. It is a 

 rudely finished bar, which has sunk below the horizon of utility, if it 

 was ever above it, and is now facing ultimate effacement. The re- 

 duction has advanced further in the male, with no improvement 

 towards regularity of outline. Here it becomes quite certain that 

 effacement advances from all sides, leaving but a small remnant of a 

 bar confined to two or three feathers. 



Glancing at the wing as a whole, in both young and old, it is plain 

 that the process of obliteration is in progress over the entire checkered 

 area. The elongated, sharp-pointed marks of the earlier pattern 

 have rounded tips in the adult; the posterior bar is roughly emargi- 

 nated; the number of checkers is reduced by a half or more; and some 

 of the remaining ones are but little more than mere dots. It is also 



1 In the young, the checkers of this row are more numerous and much more 

 sharply pointed at the ends. In both respects the Juvenal pattern approaches 

 more nearly a condition of general uniformity. 



