2JIOGS AND TOADS. 345 



explained in treating of that group, and which have been considered to foreshadow the lungs of the 

 higher animals. 



The existing Amphibia are classified in three great groups or orders. In one there is no tail 

 present in the perfect animal, although it is present in the tadpole or immature state. These are 

 called the ANOURA, or Tailless Batrachia, and they are the Frogs and Toads. 



The next group contains the Amphibia, which have tails throughout their whole life. These are 

 the URODELA, and they are subdivided into those which have either the branchiae (or gills), or else 

 gill-clefts, external throughout life the Ichthyoidea ; and into those which have neither branchiae 

 nor gill-clefts in adult age the Salamandrinse. The third order is that of the legless Amphibia, which 

 are called APODA. The Salamandrinae have the vertebrae concave behind, and eyelids, and the other 

 group of the Urodela has biconcave vertebrae and no eyelids. 



THE ORDER ANOURA. THE FROGS AND TOADS. THE TAILLESS 



BATRACHIANS. 



The Tailless Batrachians, or the Batrachians proper, or the Frogs and Toads, have a broad head, 

 largest behind, and a broad short body in the perfect state, and four legs, the hinder pair being the 

 stronger, and longer than the others, and specially suited for leaping, swimming, or burrowing. Some 

 climb, and then usually there is not a web between their fore toes, the extremities of which, and of the 

 hind ones also, are dilated into round discs. But the degree of the development of the web of the 

 fore and hind extremities refers to the power of swimming. Hence, it is not always found, and its 

 size varies. Almost all undergo a visible metamorphosis, that is to say, they have a tadpole con- 

 dition in water, and change to an adult, terrestrial, and different form. 



They are found in damp places, or in the neighbourhood of water, and those living in temperate 

 climates hibernate during the winter by getting down cracks into earth, or in the mud on the floor of 

 ponds ; whilst those living in the tropics, remote from water, bury themselves deep enough in the ground 

 to escape the hot dry atmosphere. In both cases a lethargic condition prevails, until a change of 

 season. 



Their lungs consist of two large sacs, which may be expanded until the animal attains nearly twice 

 its usual size. When they dive, the lungs are emptied of air, and the respiration will cease for a couple 

 of hours, after which time a rise to the surface, to take in air, is requisite. But during the summer 

 and winter state of existence the respiration is suspended at the same time that all the other functions 

 circulation and digestion, for instance are very low, or cease. 



Many males are provided with one or two membranous throat or mouth sacs, and when there are 

 two, one is placed on each side of J the mandible ; and if there is but one, it is found between its 

 branches. In either case the sac opens into the cavity of the mouth, by two slits, and is filled 

 with air from the lungs. These sacs enable, by their contraction, a more or less loud noise to 

 be produced. The males are often distinguished by a rough swelling on their thumbs, or by short 

 conical spurs there, and, as a rule, they are more slender than the females. 



There is usually a mass of glands, called the parotids, above the tympanum on each side of the 

 neck. The skin of the body and limbs is not covered with scales or plates, and is naked and coloured. 



The food consists of insects, slugs, and womis, and some very large kinds snap up small vertebrata. 

 They seize their prey with their tongue, and draw the victim into the mouth as this organ is 

 retracted. 



Teeth are not found in the lower jaw, and only a few have a pair of tooth-like promi- 

 nences near the chin. On the other hand, the upper jaw and vomer are very frequently armed 

 with a series of simple teeth, which in the largest species assist in capturing food. There is no masti- 

 cation possible, and the prey is swallowed entire. 



On leaving the egg, the larval or tadpole state commences, and the creature has external gills for 

 a short time ; then the gills become internal, and this immature condition lasts about 100 days, and 

 during that time the internal anatomy and .physiology greatly resemble those of fish. 



They eat during the tadpole state, living on decaying water-plants and decomposing animal 

 matter, and as they breathe by gills, they have, when young, three, and usually four, gristly or more 

 or less bony gill supports, called branchial arches. 



