188 



ORTHOGENETIC EVOLUTION IN PIGEONS. 



vanished, for it is already present from the first. In all the earlier feathers we see 

 a broad, thin band or bar of dark pigment, next to the pale tip. Now, a closer 

 inspection of this and the following stages shows that this dark bar becomes gradu- 

 ally narrower and denser, and approaches the distal edge of the feather as rapidly 

 as the pale tip narrows; and when the latter vanishes, the former is left as a black 

 tip, slightly crescentic in form, and 0.5 to 0.6 mm. in width. 



At this stage we no longer have a single color-pattern before us. The first molt 

 has begun in the scapular tract, and there we see early juvenal (s), later juvenal 

 (s'), and post-juvenal feathers (s"), the latter approximating the adult condition. 

 The molt has not yet begun in the wing-coverts, but the oblique tract has belated 

 feathers that tell of progress in several degrees towards the adult pattern. We have, 

 then, intermixture and intergrading of patterns; ascending and receding characters; 



Text-fioure 32. 



Juvenal Geopelia tranquiUa (Gtl-Bl continued), age 28 days; drawn by Hayashi, Aug. 11, 1899. X 2. 



About two rows of black-tipped feathers have come in and are fast covering up the third row of original coverts. 

 The fourth row (IV) has been molted. More black-tipped feathers are now present in scapular region. Designa- 

 tions are the same as in the preceding figure (see text). 



reduction graduating to complete erasure; advance in concentration and definition; 

 in short, progressive transmutation, recession, and substitution all combined. 



The differentiating processes are at work behind the scenes. Each new feather 

 is a faithful record of just what and how much had been accomplished at the place 

 and time of its elaboration. Unfolding in age-sequence, the feathers give us some- 

 thing more than a panoramic succession of disconnected stages. Although the suc- 

 cessive pictures presented do not exhibit perfect continuity, they follow a time order 

 close enough to remind one of a "motion picture," and leave little room to doubt 

 that the process of development runs on in flowing continuity. 



Passing on to the next stage (text-fig. 32), at the age of 28 days, we find that the 

 molt has left but few of the earlier feathers (s) in the scapular tract, and only 9 of 

 the 15 lesser coverts seen in the stage of 17 days. The oblique tract is now com- 

 pleted, and consists of 20 feathers in 3 distinct rows (1, 2, 3). The anterior and 

 earlier row (1) remains the same as in the previous stage, its 6 feathers forming a 



