. Elementary textbook of economic zoology and entomology. Zoology; Insect pests. 258 ECONOMIC ZOOLOGY AND ENTOMOLOGY areas of marsh land where frogs abound. Frogs are used more than any other vertebrate in the laboratories of schools and colleges, not only because they are easily obtained but because in their structure and habits one may find illustrations of so many of the fundamental facts of zoology. The tree-frogs or tree-toads, family Hylidce, are more closely related to the toads than to the frogs. Their toes are usually provided with adhesive disks which enable them to cling to the trun
. Elementary textbook of economic zoology and entomology. Zoology; Insect pests. 258 ECONOMIC ZOOLOGY AND ENTOMOLOGY areas of marsh land where frogs abound. Frogs are used more than any other vertebrate in the laboratories of schools and colleges, not only because they are easily obtained but because in their structure and habits one may find illustrations of so many of the fundamental facts of zoology. The tree-frogs or tree-toads, family Hylidce, are more closely related to the toads than to the frogs. Their toes are usually provided with adhesive disks which enable them to cling to the trunk of a tree or other perpendicular surfaces. Their vocal sacs are. FIG. 118.—A western garden toad, Bufo halophilus. (Reduced.) large, and they make a noise out of all proportion to their size. Hyla versicolor, the most common of these tree-frogs, is green, gray or brown above, and has the power of slowly changing from one color to another so as to produce a re- markable harmony between the frog and its surroundings, thus making it almost invisible to its enemies. This change in color is brought about by the expansion or contraction of certain pigment cells in the skin. The structure and habits of the toads, family Bufonidce, have already been discussed (Chapter II). There are about fifteen species in the United States and less than one hundred species in other lands. Some of the exotic species. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Kellogg, Vernon L. (Vernon Lyman), 1867-1937; Doane, Rennie Wilbur, 1871-. New York, H. Holt and company
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