inently obliterative, like that of all the other vertebrate orders we have 

 considered. 



Most beautiful and minute, as I have said, is the picturing of lichen- 

 flecked bark on the backs of the obliteratively shaded and 'chameleonic' 

 tree toads — e. g., Hyla versicolor. Equally effective and more remarkable 

 is the picture-pattern of some grass-frogs. This pattern is closely akin not 

 only to the grass-patterns of certain birds (see for instance the ptarmigan in 

 Fig. 41, Chapter VII), but to that worn by some ground-perching moths, 

 which will be described in a later chapter. It pictures dim, grassy ground- 

 shadow overlaced with crisscrossing bright-green grass blades. The picture, 

 moreover, is one of unusual deceptive power — as everybody will agree who 

 has tried to catch these frogs amidst luxuriant grasses. Though the species 

 is of course not wholly confined to such grassy spots, its coloration fits them 

 far more closely than it fits any other sort of ground. As is almost needless 

 to say, obliterative shading is here, as in all kindred cases, the basis of the 

 obliterative effect. The more aquatic and mud-haunting frogs have perhaps 

 less highly specialized, but doubtless perfectly adapted obliterative coloration. 

 The greens and browns of shore-weeds, of still, stagnant water, of water re- 

 flecting the green shore, of mud and sticks and water-soaked dead leaves — 

 such are the prevailing colors of these frogs. These tints are arranged, more- 

 over, in a system of complete obliterative shading, culminating usually in 

 yellowish white on throat and belly. The independent patterns they form 

 are more or less obscurely-mottled, but adequately serve as generalized pic- 

 tures of the frogs' rather various muddy and watery backgrounds. Dull 

 black shadow-color is an important factor in these patterns. But neither 

 water-shine flecks of the brighter sort, nor bright brook-bottom sun-flecks 

 occur in them, so far as I know. Somewhat more specialized, again, is the 

 picturing of the leafy forest floor on certain woodland frogs, such as the pretty 

 little Rana sylvatica, already mentioned. (See Figs. 125-126.) Small as 

 this frog is, he yet wears two or three fairly definite leaj-edge-againsi- shadow 

 pictures, on his delicate pearl-brown and dusky, obliteratively shaded 



180 



