. Beginners' Zoology . Fig. 254. —Leg Mus-cles OF Frog. BATRACHIA 133 Is the skin of a frog tight or loose ? Does it have anyappendages corresponding to scales, feathers, or hair ofother vertebrates ? Is the skin rough or smooth ? Thetoad is furnished with glands in the skin which are some-times swollen ; they form a bitter secretion, and may be,to some extent, a protection. Yet birds and snakes do nothesitate to swallow toads whole. Show how both upperand under surfaces of frog illustrate protective coloration. All batrachians have large and mnncrotis blood vesselsin the skin by which gases a
. Beginners' Zoology . Fig. 254. —Leg Mus-cles OF Frog. BATRACHIA 133 Is the skin of a frog tight or loose ? Does it have anyappendages corresponding to scales, feathers, or hair ofother vertebrates ? Is the skin rough or smooth ? Thetoad is furnished with glands in the skin which are some-times swollen ; they form a bitter secretion, and may be,to some extent, a protection. Yet birds and snakes do nothesitate to swallow toads whole. Show how both upperand under surfaces of frog illustrate protective coloration. All batrachians have large and mnncrotis blood vesselsin the skin by which gases are exchanged with the air,the skin being almost equal to a third Inng. That theskin may function in this way, itmust not become dry. Using thisfact, account for certain habits oftoads as well as frogs. If a frog is kept in the dark oron a dark surface, its skin will be- 1come darker than if kept in the light (^or on a white dish. Try this experi- ment, comparing two frogs. Thispower of changing colour is believedto b
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