THE PROBLEM OF ORGANIC DEVELOPMENT. 



193 



lines ("bars") of a light color. How can we pass without a jump from one pattern 

 to the other? 



A very simple experiment will show us how this may be done. All we have to 

 do is to pull out a few of the juvenal feathers at suitable intervals of time. Their 

 places will soon be filled by new feathers of different ages (pi. 88 and text-figs. 35, 36), 



Text-figure 35. 



Juvenal Geopelia cuneala, same as B and C of pi. 88, age 44 days; drawn by Hayashi, Aug. 1899. X 2. 



Some new feathers have developed in the scapulars. The three feathers in the first two rows of coverts are now 

 much longer than the feathers they cover. The oblique feathers are only a little longer. 



Text- figure 36. 



Geopelia cuneala (Gcl-Al), age 68 days. Hatched June 14, 1899; drawn by Hayashi, Aug. 21. x 2. 



In this second plumage only one feather of the first plumage is still visible among the small coverts; elsewhere 

 the second plumage and this is like the adult. The spots are on the edges of feathers on both sides; they are irregular 

 and narrowly bordered with black. This bird and its mate have acquired the feathers of the second plumage much 

 more rapidly than Gc 1-C 1. (See photograph of this bird at this same age in text-fig. 34.) 



and these will give intermediate stages in the transformation of the cross-lines of 

 the young into the white dots of the adult. 5 The adult pattern is thus revealed as an 

 end-stage of a continuous process of differentiation. The same experiment may be 

 made in other species with similar results. 



6 The results of this experiment are apparently nowhere fully described, and illustrations of the experimental 

 results were apparently not made. The formation of the spots from the cross-lines in the feather of diffrrrnt ages are, 

 however, beautifully illustrated in the plate and figures above cited; the descriptions which accompany these figures 

 supply additional and valuable data. — Ed. 



