Chap. XIV. Birds — Gradation of Characters. 



439 



in the most perfect ocelli, traces of the junction of three or foni 

 elongated black marks, by which the ring has been formed, may 

 often be detected. The irregular sub-triangular or narrow mark 

 (d fig. 59), manifestly forms, by its 

 contraction and equalisation, the 

 thickened portion of the ring above 

 the white shade on a perfect ball- 

 and-socket ocellus. The lower part 

 of the ring is invariably 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 origi- 

 nally been thicker than tbe upper 

 mark (c). Every step can be fol- 

 lowed in the process of confluence 

 and modification ; and the black 

 ring which surrounds the ball of 

 the ocellus is unquestionably formed 

 by the union and modification of 

 the three black marks, b, c, d, of 

 the elliptic ornament. The irre- 

 gular zigzag black marks between 

 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 shading of the ball-and-socket 

 ocelli can be followed out with equal clearness. The brown, 

 orange, and pale leaden narrow zones, which border the lower 

 black mark of the elliptic ornament, can be seen gradually to 

 become more and more softened and shaded into each other, 

 with the upper lighter part towards the left-hand corner ren- 

 dered 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, between 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-coloured shades of the 

 elliptic ornaments. Thus almost every minute detail in the 

 shape and colouring of the ball-and-socket ocelli can be shewn 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. 



Fig. 60. An ocellus in an inter- 

 mediate condition between the 

 elliptic ornament and the perkct 

 ball-and-socket ocellus. 



