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Northern Wood Frog — Part 2
Structure.—Skin very smooth, finely pitted. Buttocks granulated. Broad lateral folds perforated with pits. Groove along the middle of the back. Body flat, long, and slender. Muzzle rounded. Canthus rostralis prominent. A glandular fold of skin along jaw from under the eye to the shoulder. Eyes large, prominent, facing outwards. Space between eyes equal to or greater than the width of the eyelid. Ear round, one-third to one-half the diameter of the eye; it is likely to be inconspicuous when the cheek-patch is dark. Ridge from posterior angle of eye to shoulder not prominent. Tibia ridged lengthwise. Arms and legs slender. Fingers long and slender; base of first finger greatly thickened in male tubercles under finger-joints fairly conspicuous. Foot not thick, web delicate, with two joints of fourth toe free; inner sole tubercle small, outer small or lacking.
Range.—Rana aurora occupies the Pacific Slope. It is reported from Washington, Oregon, and California. In California, where Rana Draytonii is the common frog, Rana aurora is said to be found in the high Sierras only; in Oregon and Washington, it is abundant, but is less so in many parts of these states than is Rana pretiosa.
Rana cantabrigiensis would be recognised at once as a species closely related to Rana sylvatica, the Eastern Wood Frog. It differs only slightly in colouration and general form. It can be distinguished at once by the leg measurement; the leg to the heel just equals in length the total measurement of head and body.
This frog has the same delicacy of beauty, the same gentleness and alertness of expression, possessed by the Eastern Wood Frog. It would be surprising to find any great difference in its habits. It is probably silent, except at the breeding-season, and is more thoroughly a land frog than are most of the species of Rana.
Its relationship to Rana sylvatica is also shown by its northern distribution, which provess ability to endure a lower temperature than most frogs. (Rana sylvatica is the earliest frog to appear in the spring in the northeastern United States.)
West of the range of Rana cantabrigiensis, that is, from the Great Slave Lake to Alaska, inclusive, the representative of this frog is a subspecies, Rana cantabrigiensis latiremis Cope. The leg measurement will always distinguish this frog from the Northern Wood Frog. The western form has short, stout legs, the measurement to the heel never being more than three-fourths the combined lengths of head and body (length to heel equals distance forward to eye.) There are a few other differences plainly visible; for instance, distance between the nostrils is considerably greater than the width of head between the eyes, and the webs are much larger than in either Rana cantabrigiensis or Rana sylvatica.
This Western species, when half-grown, is a frog of much beauty of form as well as of colouring and texture of skin. It is very alert and intelligent-looking, and becomes tame in captivity. When it has attained its full size, it is much less attractive in appearance. The eye, although very lustrous, seems too small for the size of the frog; the skin has toughened and coarsened until it is leathery in appearance, and is tubercular in structure and the colouring is much less delicate and beautiful.
This frog is hardy. It is partially aquatic in its habits, remaining in shallow water much of the time and taking food from under the water. It eats fish greedily, as does the Eastern Bullfrog, and therefore must prove a menace in fish-ponds.
It is a very awkward frog, because of the massive build and great length of its hind legs. When walking, it is ludicrous in appearance, and it is still more ridiculous when it captures a fish from under the surface of the water and swallows it. The frog tries to brace himself on the long hind legs so as to use the hands, both at the same time to keep the fish away from the angles of the jaws and to push it into the mouth. To brace himself against slippery mud is not easy, and besides, the frog loses his balance because both hands are lifted at once, so he makes a great kicking and splashing before he finally swallows the fish. This frog eats not only fish, but also various water-insects, tadpoles, and smaller frogs. This species is said to be one of the most cannibalistic of our North American frogs. He eats worms and air insects, also; among the latter, sow-bugs are said to be favourites.
Both male and female "talk" vigorously in a low-pitched musical voice, when they are taken in the hand so that the feet are unsupported. There is no appearance of distended vocal sacs when the frog croaks.