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:
1. _Aglossa_--Having no tongue.
2. _Phaneroglossa_--Possessed of a tongue.
The Aglossa are few in number, and belong to southern Africa and
tropical America, where the group is represented by the famous Surinam
toad, whose eggs are fixed in separate pits or "pouches" in the spongy
skin of the mother's back, where they are placed as fast as laid, by
aid of the male.
The Phaneroglossa contains several families, the first of which,
Discoglossidæ, is characterized by the round, nonprotrusible tongue,
and includes species of toads belonging mainly to the Mediterranean
region, two of which are familiar to most readers of natural histories.
It may be well to say at this point that the terms "toad" and "frog"
do not express scientific distinctions, although generally applied by
naturalists to the first three families of the list, and especially
to the Bufonidæ; but mark the facts of popular observation that the
members of these families are more terrestrial than the members of the
families that follow them, and that they have rough warty skins in
place of smooth and shiny ones; but many exceptions confuse both the
classification and the use of the words--as, for example, in the case
of the hylas, which you may call either "tree frogs" or "tree toads,"
according to your liking.
The two species mentioned above are the "unke," or firebellied toad
of Germany, which when alarmed displays its scarlet underparts by a
peculiar attitude calculated to surprise and frighten away an enemy.
The other is the "midwife toad," most common in Spain and Portugal.
The spade-foot toads (Pelobatidæ) are a strangely distributed family
inhabiting the western United States, Mexico, eastern Europe, and the
Indo-Malayan region. Their special characteristic is the fact that
the inner tarsal tubercle is large and is transformed into a shovel,
which is covered with a hard, sharp-edged, horny sheath. Having this
excellent tool these small and noisy toads rapidly excavate deep holes
in the soil, preferring sand, and lie hidden during the day, but come
forth at night to hunt. They resort to water only for a week or so
of egg-laying in the spring, and remain unknown to most persons in
whose neighborhood they are really numerous. Our common American one
(_Scaphiophus solitarius_) is about two inches long, and brown above
with darker patches.
This brings us to the typical toads, Bufonidæ, represented in all parts
of the world except certain islands. A hundred pages might be filled
with interesting accounts of the manners and customs of the hundred or
so species, many very different from those familiar to us.
All breed in water, resorting to ponds and pools in the early spring.
Where many broods have hatched the young can be met with in myriads,
the ground literally swarming with them; and as they are naturally
stirred up by a sudden warm rain, perhaps after a drought, people will
occasionally affirm as an observed and well-ascertained fact that "it
has rained toads"--something that never occurs except in the very rare
cases when a cyclone has scooped the water and everything in it out of
a pond and scattered it abroad.
Most of these young, migrating toads disappear as food for birds,
snakes, etc., or die of disease. The food of young and old consists of
insects, worms, snails, and the like; and it is an easy thing to tame
toads and have much amusement in watching them at work in the early
evening, for they are crepuscular in habits; and the wise gardener will
see that they are not disturbed in their beneficial service of catching
and devouring insect pests, unless they are so numerous as to be a
nuisance.
The smallest North American toad is the oak toad of the Southern
States, which is only an inch long. When, in the breeding season, these
diminutive toads flock to the pools in great numbers, they keep up an
ear-splitting chorus of shrill _peeps_, like so many young chickens.
FROGS AS NURSERY MAIDS AND WEATHER PROPHETS
The tree frogs are a very large family (Hylidæ) distributed all over
the world, except Africa, but most of the species belong to the
steamy forests of tropical America. All are of small size, have smooth
skins, normally greenish, but very changeable in color to adapt the
creatures to the hue of their surroundings, as a protective device;
and most of them inhabit trees. To enable them to do this the toes end
in expanded, padlike disks, the contraction of which, when the foot
is pressed against a surface, produces one or more furrows and, in
addition, causes the exudation of a little mucilaginous liquid. The
foot pressed against the surface expels the air, and this fact, aided
by the stickiness of the pad, enables the frog to hold on to even a
vertical plane of glass. All Hylidæ have a voice, often very loud, and
enhanced by membranous sacs under or on each side of the throat, or in
some cases internal; this sac, when blown out may be almost as large
as the creature's body, as may be seen in our common gray tree frog
when "singing." This species, like most others, becomes very noisy in
the evening, in cloudy weather and before rain, with its not unmusical
croaking; and a similar European species is kept in confinement by some
people as an interesting pet and weather prophet.
The most interesting thing about the Hylidæ is their various methods of
breeding, for while most of them lay their eggs, up to a thousand in
number, in the water, many produce but a few, and attach them to the
body.
A large tree frog called in Brazil "ferreiro" (smith), makes a sound
like a mallet slowly and regularly struck on a metal plate. This frog
actually builds a nursery in the shallow edge of a pond, where a
basin-shaped hollow, with a rim, is formed by the broad-handed female.
Here she leaves her eggs, safe from egg-eating fishes or insects, as
the rim forms a wall higher than the surface of the water. A Japanese
frog makes a similar basin, then produces a liquid which she kicks into
a froth, and into the midst of this the eggs are dropped, and there the
hatched larvæ develop, and remain until the gradual collapse of the mud
rim sets them free.
In these and similar cases the eggs and tadpoles are abandoned by the
parents; but many frogs watch over and care for their young. Some carry
the young in a pouch on the back, but how it is accomplished is not
known. A West African species carries its eggs in its mouth; and the
male of Darwin's frog, of Chile, carries the eggs in a great vocal
pouch beneath its throat, which subsequently forms a nursery for the
tadpoles until they emerge as young frogs.
It must be noted, however, that some of these examples belong to
the related family Cystignathidæ--a very extensive family largely
represented in Central and South America.
The remainder of the tailless amphibians are assembled in the numerous
and widely distributed family Ranidæ, which is that of the "true"
frogs. The typical subfamily, Raninæ, is cosmopolitan, except as to
Australia and South America south of the Amazon basin; but some less
typical forms are confined to the tropics, and include several strange
species, such as the little arboreal Dendrobates frogs of Brazil, one
of which is famous for furnishing in the secretion of its skin a dye
that when properly applied turns the green plumage of tame parrots into
yellow--a fashionable tint. These small and pretty frogs are noted for
their solicitude for their young, carrying baby tadpoles on their
backs--where the infants creep and become attached--from place to
place, as safety or better water conditions suggest.
The North American frogs are good examples of the ranine race, and
those more commonly seen are the following:
Leopard frog (_Rana pipiens_), green with irregular black blotches,
mostly in two rows on the back; legs barred above; belly pale. Eastern
specimens are more olive than bright green.
Pickerel frog (_R. palustris_), light brown with two rows of large,
oblong, square blotches of dark brown on the back, a brown spot above
each eye, and a dark line from the nostril to the eye; upper jaw white
and black. Habitat, eastern United States among mountains.
Wood frog (_R. sylvatica_), pale reddish brown; a black band across the
pointed face. This smallest of our species is to be found only in damp
woods, resorting to water only in early spring to deposit its eggs; and
it is almost silent.
Green, or spring frog (_R. clamatans_), green or bronze-brown, brighter
in front, with more or less small black spots; yellowish white below.
This is a rather solitary frog, living in springs and small ponds,
where it utters the familiar "chung" at frequent intervals. It is
distinguished by the enormous size of its eardrum.
Bullfrog (_R. catesbiana_), greenish, brightest on the head, and with
small dark spots on its back; legs blotched; eardrum large; toes
broadly webbed. Length five to eight inches, breadth four to five
inches. It utters a roar not unlike that of a distant bull, and a
company of them on a still summer evening will awaken the neighborhood.
Bullfrogs are present throughout the eastern United States and Canada,
west to the dry plains; and furnish the market with "saddles" (their
hind legs) as a table delicacy when fried. These frogs may lay 12,000
eggs apiece.
All our frogs lay their eggs in water in rounded masses, not in
strings, as do the toads, usually attached to some submerged stick or
plant stem. The tadpoles, light in color, are very voracious, and feed
on every sort of flesh that they can bite off and chew with their horny
jaws. On the approach of winter the frogs--except the wood frog, which
hibernates in the loam of the forest, or in some rotten stump--sink
into the mud of the pond or marsh where they live, and pass the cold
months in torpidity. Their food is almost exclusively insects, caught
by the tongue, but the big bullfrogs seize with their mouths any small
creature that comes their way.