562 THE DESCENT OF MAN 



left hand upper corner, the feather being held erect, in 

 the position in which it is here drawn. Beneath this thick- 

 ened part there is on the surface of the ball an oblique 

 almost pure white mark, which shades off downward into 

 a pale leaden hue, and this into yellowish and brown tints, 

 which insensibly become darker and darker toward the 

 lower part of the ball. It is this shading which gives so 

 admirably the effect of light shining on a convex surface. 



If one of the balls be exam- 



S jt-i jf'\', ■*'*v,'^y8i i^s<^) i* ^^^^ ^® seen that the 



U ri * * * 1 1» "Xl •■' ^«l lower part is of a brown tint 



^% t'"'' " f, ' 'Ss' VvX'tf ^^^ ^^ indistinctly separated by 



^ ^i '? " i i' 'J ^ curved oblique line from the 



\ji/* ''\' iV,^ * .^ upper part, which is yellower 



^^l ■ "' '^' **' ',, i •*/ and more leaden; this curved 



y '. ■'**'.'*"!/ oblique line runs at right angles 



'f , - '., ' ' *3j ^ , fj to the longer axis of the white 



i ' ** 'Vi '* *i^J*"^t pa-tc^ of ligH and indeed of 



\v» A^' %'''^^'^^) ^^^ *^® shading; but this dif- 



*Clu»' iis'\r ' ■*!» ference in color, which cannot, 



Y^'" f'-"^ "" , of course, be shown in a wood- 



e^^jj ,*•' ' 'y cut, does not in the least inter- 



\t" ■<[|i ,* , fere with the perfect shading of 



j! ' ^ the ball. It should be particu- 



A^^ larly observed that each ocellus 



FiQ. B8.-Basai part of the secondary stands in obvious Connection 



wing-feather nearest to the body. , ,-, •.^ -t ^ , . „ 



either with a dark stnpe, or 

 with a longitudinal row of dark spots, for both occur in- 

 differently on the same feather. Thus in Fig. 57 stripe A 

 runs to ocellus a; B runs to ocellus b ; stripe C is broken 

 in the upper part and runs down to the next succeeding 

 ocellus, not represented in the woodcut; D to the next 

 lower one, and so with the stripes E and F. Lastly, the 

 several ocelli are separated from each other by a pale sur- 

 face bearing irregular black marks. 



I will next describe the other extreme of the series; 

 namely, the first trace of an ocellus. The short secondary 



