BIRDS-GRADATION OF CHARACTERS. 



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'41 

 A. 



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(d. fig. 59), manifestly forms, by its contraction and equalization, 

 the thickened portion of the ring above the white shade on a per- 

 fect ball-and-socket ocellus. The lower part of the ring is invari- 

 ably a little thicker than the other 

 parts (see fig. 57), and this follows 

 from the lower black mark of the 

 elliptic ornament (b fig. 59) having 

 originally been thicker than the 

 upper mark (c). Every step can bei 

 followed in the process of conflu- 

 ence and modification; and the 

 black ring which surrounds the ball 

 of the ocellus is unquestionably 

 formed by the union and modifica- 

 tion of the three black marks, b, c, 

 d, of the elliptic ornament. The 

 irregular zigz%g black marks be- 

 tween the successive ocelli (see 

 again fig. 57) are plainly due to the 

 breaking up of the somewhat more 

 regular but similar marks between 

 the elliptic ornaments. 



The successive steps in the shad- 

 ing of the ball-and-socket ocelli can 

 be followed out with equal clear- 

 ness. The brown, orange, and 

 pale leaden narrow zones, which 

 border the lower black mark of 

 the elliptic ornament, can be seen 

 and more softened and shaded 

 upper lighter part towards the left-hand corner rendered still 

 lighter, so as to become almost white, and at the same time more 

 contracted. But even In the most perfect ball-and-socket ocelli 

 a slight difference in the tints, though not in the shading, be- 

 tween the upper and lower parts of the ball can be perceived, as 

 before noticed; and the line of separation is oblique, in the 

 same direction as the bright-colored shades of the elliptic orna- 

 ments. Thus almost every minute detail in the shape and color- 

 ing of the ball-and-socket ocelli can be shown to follow from 

 gradual changes in the elliptic ornaments; and the development 

 of the latter can be traced by equally small steps from the union 

 of two almost simple spots, the lower one (fig. 58) having some 

 dull fulvous shading on its upper side. 



The extremities of the longer secondary feathers which bear 

 the perfect ball-and-socket ocelli, are peculiarly ornamented (fig. 

 61). The oblique longitudinal stripes suddenly cease upwards 



29 





Fig. 60. An ocellus in an 

 intermediate condition be- 

 tween the elliptic orna- 

 ment and the perfect ball- 

 and-socket ocellus. 



gradually 

 into each 



to become more 

 other, with the 



