122 ORTHOGENETIC EVOLUTION IN PIGEONS. 



in the first feathers of young robins are of some interest. I made an examination 

 of the feathers of some young robins shortly after reviewing Hacker's paper, 18 and 

 find that their markings verify results obtained on the pigeons. I have taken 

 feathers from the same points in three individuals for reproduction (pis. 56 and 57). 



Hacker's figures 1 and 14 represent, as he believes, two of the "most primitive 

 types of marking"; the latter, being slightly lower in the scale of development, has 

 "as a rule, no light edge." I find both types represented on the young robin, and 

 the "light edge" is generally quite plain, although it is often narrow, and sometimes 

 so weak that it would escape attention if not kept in mind and carefully looked for. 

 I find this "edge" best represented in the median wing-coverts (next in front of 

 the long coverts) and scapulars. 



Hacker was aware that these two forms are essentially one, as they often replace 

 each other in corresponding areas. My figures demonstrate this conclusively (pi. 

 56, fig. 1, in each i, n, and in, from middle upper breast). 



In the second series (in b of pi. 57) the clear edge is 0.5 mm. wide, and the black 

 bar is about 1 mm. in width. The clear edge is widest where the clear center is 

 widest; narrowest where the clear center becomes a mere line, as in plate 56, 

 figure i b. 



In the mid-back, between the scapulars, the clear edge is obsolescent in i « and 

 ii a (pi. 57) requiring a lens to discover it, and is only just visible to the naked eye 

 in in a. Notice here (in a) that by extension of basal gray pigment the light middle 

 area becomes simply a wide transverse bar. We have the order thus: first, a rudi- 

 mentary apical light bar; second, a black bar; third, a light pale-yellowish bar. 



In the second series c.c.c. and d.d.d.— the figures are of median and long wing- 

 coverts — the "median streak" is continuous with the light-buff tips. There is here 

 no subterminal black bar. It looks as if the black had vanished, thus bringing the 

 median streak and the apical light edge together. In d.d.d. the median streak is 

 absent in i, largest in m. 



The clear or light edge can not be made out on the first series (pi. 56) on i 1 and 

 ii 1, but it is faintly present on the tips of about four of their barbs; in 2, from mid- 



18 Before the Zoological Seminar, May 13, 1903. 



Explanation of Plate 56. 



Selected feathers from the juvenal robin, Merula migratoria, age 3 weeks. x 1.6. Toda del., May 

 1903. 



First series. — Three rows of feathers from three robins (I, II, III): 

 Under side of body: 



In the three birds I have the shaft-streak scarcely wider than the shaft itself; in II the streak is widened, and in 

 III it, is widest — about 1.5 mm. at widest part. The narrower this streak the darker the bird as a whole. So my 

 three birds represent three degrees that probably show the average in II. 

 Figure I 1. From mid-upper breast. 

 Figure I 2. From mid-lower breast. 



Figure I 3. From abdomen; a small apical dark spot or edge, or no dark edge (III 2). 



Figure I 4. From bunch of flank feathers just above the upper half of leg, mostly covered by wing (right side). 

 Figures II 1, 2, 3, 4. From corresponding points in a second individual. 

 Figures III 1, 2, 3, 4. From corresponding points in a third individual. 



Third series. — Single row of outer scapulars from before backwards (IV) : 

 Figure IV 1. Anterior scapular. 

 Figure IV 2. Front of middle scapular. 

 Figure IV 3. Behind middle scapular. 

 Figure IV 1. Posterior feather. 



See text for further explanation. 



