Nearly allied to the Toads, Bufo, the Surinam Toad, Pipa, holds its place. Its physiognomy is at once hideous and peculiarly odd: the head is flat and triangular, a very short neck separates it from the trunk, which is itself depressed and flattened. Its eyes are extremely small, of an olive, more or less bright, dashed with small reddish spots. It has no tongue. There is only one species of Pipa, viz. the American Pipa ([Fig. 8]), which inhabits Guiana and several provinces of Brazil. The most remarkable feature in this Batrachian is its manner of reproduction. It is oviparous, and when the female has laid her eggs, the male takes them, and piles upon the back of his companion these, his hopes of posterity. The female, bearing the fertilized eggs upon her back, reaches the marshes, and there immerses herself; but the skin of the back which supports the eggs soon becomes inflamed, erysipelatous inflammation follows, causing an irritation, produced by the presence of eggs, which are then absorbed into the skin, and disappear in the integument until hatched.
The young Pipa Toads are rapidly developed in these dorsal cells, but they are extricated at a less advanced stage than almost any other vertebrate animal. After extrication, the tadpole grows rapidly, and the chief change of form is witnessed in the gills. As to the mother Batrachian, it is only after she has got rid of her progeny that she abandons her aquatic residence.[9]
The Batrachians differ essentially from all other orders of Reptilia. They have no ribs; their skin is naked, being without scales. The young, or tadpoles, when first hatched, breathe by means of gills, being at this stage quite unlike their parents. These gills, or branchiæ, disappear in the tailless Batrachians, as the Frogs and Toads, in which the tail disappears, are called. In the tadpoles the mouth is destitute of a tongue, this organ only making its appearance when the fore limbs are evolved. The habits also change. The tadpole no longer feeds on decomposing substances, and cannot live long immersed in water. The branchiæ disappear one after the other, by absorption, giving place to pulmonary vessels. The principal vascular arches are converted into the pulmonary artery, and the blood is diverted from the largest of the branchiæ to the lungs. In the meantime the respiratory cavity is formed, the communicating duct advances with the elongation of the œsophagus, and at the point of communication the larynx is ultimately developed. The lungs themselves extend as simple elongated sacs, slightly reticulated on the inner surface backwards into the abdominal cavity. These receptacles being formed, air passes into and expands the cavity, and respiration is commenced, the fore limbs are liberated from the branchial chambers, and the first transformation is accomplished.
The alleged venemous character of the Common Toad has been altogether rejected by many naturalists; but Dr. Davy found that venemous matter was really contained in follicles in the true skin, and chiefly about the head and shoulders, but also distributed generally over the body, and on the extremities in considerable quantities. Dr. Davy found it extremely acrid, but innocuous when introduced into the circulation. A chicken inoculated with it was unaffected, and Dr. Davy conjectures that this acrid liquid is the animal's defence against carnivorous Mammalia. A dog when urged to attack one will drop it from its mouth in a manner which leaves no doubt that it had felt the effects of the secretion.
In opposition to these opinions the story of a lad in France is told, who had thrust his slightly wounded hand into a hole, intending to seize a Lizard which he had seen enter. In place of the Lizard he brought out a large Toad. While holding the animal, it discharged a milky yellowish white fluid which introduced itself into the wound in his hand, and this poison occasioned his death; but then it is not stated that the boy was previously healthy.
Warm and temperate regions with abundant moisture are the localities favourable to all the Batrachians. Extreme cold, as well as dry heat, and all sudden changes are alike unfavourable to them. In temperate climates, where the winters are severe, they bury themselves under the earth, or in the mud at the bottom of pools and ponds, and there pass the season without air or food, till returning spring calls them forth.
The species of this family are very numerous. MM. Duméril and Bibron state that the Frogs, Rana, number fifty-one species; the Tree Frogs, Hyla, sixty-four; and the Toads, Bufo, thirty-five. They are found in all parts of the world, the smallest portion being found in Europe, and the largest in America. Oceania is chiefly supplied with the Tree Frogs. There are several curious forms in Australia, and one species only is known to inhabit New Zealand. The enormous fossil Labyrinthodon, of a remote geological era, is believed to have been nearly related to these comparatively very diminutive Batrachians.[10]
Tailed Batrachians,
Sometimes called Urodeles, from ουρα, "tail," δηλος, "manifest." The constant external character which distinguishes these Amphibians in a general manner is the presence of a tail during the whole stage of their existence. Nevertheless they are subject to the metamorphoses to which all the Amphibians submit. "The division, therefore, of reptiles," says Professor Rymer Jones, "into such as undergo metamorphoses and such as do not, is by no means philosophical although convenient to the zoologist, for all reptiles undergo a metamorphosis although not to the same extent. In the one the change from the aquatic to the air-breathing animal is never fully accomplished; in the tailed Amphibian the change is accomplished after the embryo has escaped from the ovum."
Salamanders have had the honour of appearing prominently in fabulous narrative. The Greeks believed that they could live in fire, and this error obtained credence so long, that even now it has not been entirely dissipated. Many people are simple enough to believe from the Greek tradition that these innocent animals are incombustible. The love of the marvellous, fostered and excited by ignorant appeals to superstition, has gone even further than this; it has been asserted that the most violent fire becomes extinguished when a Salamander is thrown into it. In the middle ages this notion was held by most people, and it would have been dangerous to gainsay it. Salamanders were necessary animals in the conjurations of sorcerers and witches; accordingly painters among their symbolical emblems represented Salamanders as capable of resisting the most violent action of live coal. It was found necessary, however, that physicians and philosophers should take the trouble to prove by experiment the absurdity of these tales.