wings and tails are almost always very translucent, and contrast brightly with 

 the opaque dusky bands, even when the wing or tail is seen from below, and 

 deeply shadowed. As the pictures show, the dark marks are just of one 

 'value' with the darker twigs and branches, and the light bands between of- 

 one value with the interspaces of foliage transfused with skylight, against 

 which the branches and twigs 'relieve.' 



Another noteworthy detail of the independent efficacy of pattern is the 

 masking of birds' and mammals' eyes * Markings of this kind occur chiefly 

 on predatory mammals, and on birds. See, for instance, the young plover's 

 head in Fig. 67. Notice the dark ring surrounding the eye, and the longi- 

 tudinal dark mark at either end of it— a 'stringing out' of the eye's dark 

 tone. Patterns like this, but often bolder and more varied, surround the 

 eyes of many birds and a few quadrupeds. The lengthwise stripe, especially — 

 the dark line which the eye seems scarcely to interrupt — is a very common 

 marking among birds. This seems to be a 'conventionalized' eye-masking 

 pattern, like the conventionalized ground pattern of larks and sparrows. It 

 is very effective, however, as it completely breaks the eye's otherwise conspic- 

 uous circular or oval outline. Other, more varied patterns achieve this in a 

 still higher degree, often seeming to absorb the eye into themselves as one of 

 the details of their irregular form. (See Figs. 67-72.) Light-colored eyes, 



* Many herbivorous mammals have dark and lustrous eyes, surrounded by a more or less dis- 

 tinct pale-colored ring. This, however, belongs to the obliterative shading, playing its full part of 

 shadow-neutralizing when the eye is shut. Very likely the noticeableness of the open eye does the 

 animal good service when it is skulking, inasmuch as it increases the likelihood that the skulker will 

 know the instant he is surely detected by an enemy. All the rest of him is almost or quite 'oblit- 

 erated,' but there is still much chance that a predatory creature, hunting by scent as well as by sight, 

 may discover him. Because of this chance, he must be alert, ready to leap and run at any moment, 

 and must keep his eyes open, even though they may help to reveal him. But their very conspicu- 

 ousness increases the chance that the predator, having followed his quarry up by scent, or coming 

 suddenly upon it, will look first directly at those its points of vital watchfulness, thus giving it the 

 beneficent timely warning — the sure and instant signal that the crouching £ game is up ' — which would 

 be lacking if the hunting-beast first recognized some other portion of its quarry's body. Encircling 

 marks and all, the eyes are small details of the 'obliterated' creature, and cannot attract the pred- 

 ator's attention unless he comes almost within striking distance. 



81 



