52 ORTHOGENETIC EVOLUTION IN PIGEONS. 



straight-cut outline. The less black in the wing as a whole, the more serrate this bar, as 

 a rule; the more black, the more the long point fills up towards the straight-cut form. 



(3) In the first plumage of young domestic doves I find that the second bar generally 

 exhibits pointed spots, and more strongly pointed as we descend from the back where 

 the spots are most developed and most nearly straight to the lower edge of the wing, 

 where the spots disappear, or become much less developed and increasingly pointed. In 

 the second plumage these spots become fuller and less pointed, often losing all marked 

 serration. 



(4) The first plumage of passenger-pigeons and the adult plumage of passenger females 

 contains well-marked serrate bars, which are more or less lost in the adult males the 

 males having a more nearly uniform color than the females and young. 



(5) The young of Geopelia humeralis have the long-pointed spots in the first plumage. 

 In the second plumage they are wholly absent. 



(6) The fact that the element of the bars is so generally distributed among wild species 

 and that it generally takes the pointed form, or a form plainly derived from the pointed 

 type, is a strong evidence that the pointed spot is the archaic form. 



(7) On any other assumption, what explanation do we have for the pointed pattern 

 in so many wild species, and especially in the first plumage of pigeons? Evidently we must 

 have a view consistent with some sort of evolution of the bars. If the pointed spot is not 

 the original element, then what is more so? 



(8) Two bars are nowhere indicated to be the original number; on the contrary, the 

 evidences are for more or less even distribution of the spots over the wing and scapulars. 

 It is, in fact, easy to find many different species with many bars in progress of evolution, 

 but no species where these marks are limited to two, as in some of the Columba livia. 



In the other form a barred wild rock with traces of a third bar the tertials and 

 secondaries (14 in number) graduate into one another in form and color-marks so that no 

 dividing-line is possible (pi. 2). This (first) bar is' compounded of two distinct bars, 

 one being terminal (secondaries), the other subterminal (tertials). The upper, subterminal 

 bar continues from the fourteenth feather to the fifth; the terminal from tenth to the 

 first. The two, therefore, are present together on the tenth to the fifth i.e., on 6 middle 

 feathers the lower 4 secondaries having only the terminal, while the upper four tertials 

 have only the subterminal bar. On the middle six feathers (10 to 5), the terminal bar 

 diminishes upward, while the subterminal diminishes downward. 



In some of my domestic pigeons both bars extend farther, the terminal running up on 

 the tips of the tertials, the subterminal running down across the lower secondaries and even 

 across the primaries in diffuse freckles. The extension in opposite direction is the later 

 development. 



We have, in this (first) bar, double spots (upper and lower) on the upper four feathers 

 and a trace on the tenth ; the spots of the subterminal bar average about twice the length of 

 the spots of the second bar. 



The subterminal bar alone is the serial homologue of the anterior bars, while the terminal 

 bar is not represented in the anterior feathers except for a bare trace, as seen in young 

 domestics. This trace is very interesting, showing that there is a tendency to repeat the 

 same pattern in each feather, and if the pattern is reduced it is the weaker position that 

 suffers first; e.g., the anterior bar disappears before the second or first; the lower parts fail 

 of development sooner than the upper parts. Reduction of development leaves the pattern 

 in a more ancient form that is, in elongated spots, rather than square or rounded spots. 



In looking at the first bar of a young domestic pigeon, I notice that in the folded wing 

 only the upper ten feathers secondaries and tertials take part in forming the visible 

 portion of the bar (i.e., the subterminal bar). The lower four secondaries have the spots 

 diminishing in extent and depth of color downward and each showing the original pointed 



