FROGS AND TOADS. 435 



gradually diminishing, both in size and numbers, in the temperate zones, and 

 being unknown in the polar regions, as indeed they are in deserts. Although 

 members of the class are found in all regions except those named, the orders 

 are by no means evenly distributed. In the Northern Hemisphere, for in- 

 stance, salamanders and newts are abundant, and the burrowing forms, known 

 as csecilians, are wanting ; whereas in the Southern Hemisphere csecilians 

 occur, but salamanders and newts are totally unknown. Among the frogs 

 and toads certain families are confined to particular areas, but it is remark- 

 able that there are indications of distinct relationship between certain groups 

 respectively restricted to South America and Africa south of the Sahara. 



ORDER I. ECAUDATA. 



FROGS AND TOADS. 



THE frogs and toads constitute one Order, all the members of which are 

 easily recognised when adult by the short and often plump form of the body, 

 the total absence of a tail, and the presence of four fully-developed limbs, the 

 hind pair being generally much longer than the front ones. Even more strik- 

 ing features are displayed by the skeleton. Instead of continuing to the end 

 of the body, the backbone proper stops short about the middle of the back, 

 and never comprises more than eight vertebra). Beyond this it is continued 

 as a long, tapering, un jointed rod. To the extremities of the horizontal 

 transverse processes of the last, or sacral vertebra, are articulated the anterior 

 ends of the greatly elongated ilia of the pelvis, these bones running as far 

 backwards as the hinder end of the aforesaid rod, where they bear the sockets 

 for the articulation of the uppermost bone of the hind-legs. By this very 

 peculiar, and indeed unique arrangement, the setting-on of the hind-limbs is 

 carried far behind the sacrum. The radius and ulna in the fore-limb, and the 

 tibia and fibula in the hind-limb, are respectively united to form a single 

 bone, and the elongation of the hind-legs is produced by the lengthening "of 

 those bones in the ankle-joint known as the astragalus and calcaneum, so as 

 to form a pair of parallel long bones. Like all other living members of the 

 class in which both limbs are fully developed, frogs and toads have four front 

 and live hind-toes. In the tadpole stage which is occasionally suppressed 

 the hind-limbs bud before any trace of the front pair is visible. Usually 

 this stage of existence is passed entirely in the water, but there are some very 

 peculiar forms in which the young are produced in the moist foliage of leaves. 

 On land the adults of the tailless batrachians progress either by taking long 

 leaps from the hind-legs or by dragging forwards first one and then the other 

 of these, and thus pushing the body along. In swimming, the hind-legs are 

 alone employed for propulsion, the front pair being pressed close to the chest. 

 The total number of species of the tailless amphibians probably does not fall 

 far short of a thousand, and representatives of the group are found in all 

 countries suitable to the existence of amphibian life- Curiously enough, the 

 largest forms are found in some of the islands of the Pacific. Whereas the 

 majority are terrestrial, a considerable number have adopted an arboreal life. 

 The group is divided into twelve families, of which the two last differ from all the 

 rest in the absence of the tongue. Unfortunately, the characters by which the 



