Otherwise our salamanders are small species found in brooks, ponds, and wet woods, and often getting into cellars and wells. Uninformed persons think them to be lizards, and foolishly fear them, but except for the irritation of the hands that may follow rough handling they are utterly harmless to man or his property, and serve him by devouring great quantities of insects and worms.
A common species in damp, neglected woodlands is the little red-backed fellow that is so light and leaping in its movements when disturbed, even throwing off its tail in its panic of fear. It is more terrestrial than most, laying its few eggs in rotting wood instead of going into the water for that purpose; and the young carry gills but a few days. This red-backed Plethodon must not be confused with the small newts, bright vermilion with a row of glowing spots along the sides, that are found in woods in summer. They are young specimens of Diemyctylus viridescens, which is common all over the eastern part of the United States and southern Ontario. The parents are green, and wholly aquatic in habits. The larvæ have gills and swim about until early autumn, by which time their gills have been gradually absorbed, and they go ashore, where their coats change in color from a mottled green to scarlet. This red condition and their residence on land continue until the autumn of the third, or the spring of the fourth year of their lives, when they become sexually mature, resume a greenish dress, go back to the water, and pass the rest of their lives there.
Mention can be made of only one more species—the black, yellow-spotted "tiger triton," which is the most widely spread and often seen of our terrestrial salamanders. It is especially noteworthy because of the extraordinary condition of suspended development exhibited by its larva, the famous edible axolotl of Mexican lakes, which, while still retaining larval gills and aquatic habits, grows nearly or quite to the size of its parents—three to four inches—and becomes capable of breeding. Similar cases are known in certain lakes in southern Europe; and it appears that this arrested development, together with natural growth of body, occurs occasionally in many other amphibians. The condition is termed "neotony," but the biological explanation of it is not clear.
[CHAPTER XIX]
AMPHIBIANS—Continued
FROGS, TOADS AND TADPOLES
The frogs and toads of the order Anura differ from the inferior batrachians principally in form. The tail is absent, and instead of long, slender bodies and small legs, or none, they have short, squat, triangular bodies and hind legs, at least, of relatively great size and strength, whereby they progress when on land by leaps instead of by running or creeping; some are almost wholly aquatic in habit, others almost wholly terrestrial or arboreal. The ossification of the bones is far more complete, the eyes and ears (represented by the large tightly drawn membrane, the "tympanum," on each side of the head, covering the internal ear) are well developed, and the voice is louder than in the urodeles, which can do little more than squeak. The mouth is usually large and cleft to beyond the eyes. The tongue, used to capture prey, is not thrust straight forward, but thrown "overhand," as it were, catching the insect aimed at in its curling and sticky tip.
All frogs and toads are flesh eaters, mainly of worms and insects and larval or small water animals; but the big species, such as the bullfrog, may seize prey of considerable size as it comes within reach, such as young ducklings. None hunt about for prey, but, aided by the concealing nature of their colors, wait quietly until a victim comes within reach of their quick and accurate tongues. All lay their eggs in still water, varying in number from a few score to several thousands, according to the species. In all cases the young are hatched in a larval form, called "tadpole," having a tail and gills, and this gradually changes into the adult, tailless form of the adult. On emerging from the egg the embryo has a very large head and body. In a frog the external gills and the long, compressed tail are only feebly developed when the tadpole is first hatched, while the mouth is provided with a much developed adhesive apparatus, by means of which the young attach themselves to plants or other objects. The tadpole changes by regular stages into the adult form, the tail being slowly absorbed into the body from which the legs grow out.
The Anura are separable into two suborders: