1901.] EVOLUTION or PATTEBN IN PEATHBRS. 317 



between the two horns has been filled in. Pigs. 9 and 10 show a 

 further stage in the gradual cutting-off of the upper part of the 

 spot to form a bar \ I'igs. 11 and 12 represent two other stages 

 in another line of development, showing the formation of the 

 crescent. 



Disregarding the pattern for a minute we may turn to the 

 question of colour, and imagine the typical feather with its dark 

 bars. At first, as I mentioned above, there is a slight tinge of 

 lighter colour towards the upper margin of the feather (not shown 

 in the figure) ; in other specimens we notice that the dark bars 

 are narrower, and that the hghter colour has a reddish tinge and 

 appears on both sides of the bars. In another specimen, again, the 

 bar is still narrower, and the red darker and overspreading a 

 much larger area, while what is left of the bar has, so to speak, 

 been unevenly eaten away, so that merely a thin vermiculated stripe 

 is left ; and finally the feather is almost entirely suffused with red 

 which is rather more intense where the bars were ; this last stage 

 being that found in some adult males. In these stages, however, 

 although the intensity of the red may vary considerably, the original 

 position of the bars may always be traced. 



Lest I should be misunderstood, I would mention that in all 

 these cases the feathers have been taken from different birds, and 

 that I have no proof of the pattern on any individual feather being 

 changed as some writers (cf. E. B. Sharpe, P. Z. S. 1873, p. 44) 

 have suggested : it may be so, or it may not, but that contingency 

 has not been taken into account in this paper. 



I propose now to make a few deductions from these various 

 patterns, and then, if possible, prove them to hold good by taking 

 examples from various species in widely different Orders. 



Pirst, I would suggest that the most primitive feathers were 

 entirely colourless, or of a dull dingy grey, the first trace of a 

 pattern being a longitudinal stripe of colour down the rhachis. 

 Possibly the feathers of some species became self-coloured without 

 undergoing any pattern stage, but this is doubtful ; and in the 

 majority of self-coloured birds, even when white, the self-coloration 

 has been subsequently assumed. The self-coloured feathers are 

 those in which it is most difficult to fix the period of evolution. 

 They may, for instance, be merely the very much enlarged longi- 

 tudinal stripe, as in the case of those birds whose young show light 

 edgings to their feathers. This is probably the most usual form ; 

 or they may come about by the gradual reabsorption of the bai-s, 

 the colour spreading over the entire feather ; or they may be of a 

 later stage altogether, as in the breast of G-ulls and many other 

 birds, where the light colour of the underparts has probably been 

 assumed for protection. 



The following tree will perhaps give a closer idea of the possible 

 stages in the evolution of pattern. 



^ It may be noted that in most of the figures four bars are shown, and that 

 therefore the terminal spot in figs. 7-10 probably represents the two terminal 



