406 Vertebrata. 



bony scales were developed. The siu-face of the teeth, in some of the 

 Stegocephala, has deep, compressed spiral folds, which, especially at the baaes, 

 stretch far into the mass, and in transverse section look like ciu'ved lines ; hence 

 the name Labyrinthodonta, which has been given to this group, but 

 which only suits one section of the members, since the rest have teeth of 

 simple stractui'e. 



Order .2. Anura. 



There is no projecting tail in the adult. The hind limbs, which 

 are always more powerful than the anterior, are jumping or swim- 

 ming legs, and have a larger or smaller web between the toes. Lower 

 jaw edentulous. Larva at first with external, later with internal, 

 gills. 



The young larvae (Fig. 327 A — B) are small, elongate animals, having 

 three external gills on each side, and a pair of sucker-Uke sticky organs on the 

 head, by means of which they attach themselves firmly to plants, etc. ; limbs are 

 absent. After a few days the external gills are covered by an operculum, and 

 atrophy, whilst internal giUs arise on all the gill-bars (see above, p. 398). Simul- 

 taneously the form of the body changes, head and ti-unk together become almost 

 spherical, as distinct from the powerful tail with its large fin (Kg. 327 C) ; the 

 adhesive apparatus disappears. The larva (tadpole), which has homy jaws and a long 

 coiled gut, feeds upon decayed vegetables, dead animals, or mud; it is an active 

 swimmer. Of the gradually developing limbs the anterior lie within the branchial 

 cavity dm^ng the whole of larval life ; that is to say the points at which they 

 project are covered, like the gill-bars, by the operculum. The fore limbs break 

 through the outer wall of the branchial cavity, but this only occui-s at the meta- 

 morphosis when the tail dwindles ; the teeth develop (that is if the adult has- 

 teeth), the small mouth enlarges, etc. 



1. Frogs (Rana) have teeth in the upper jaw ; a smooth skin ; round 

 pupil; long, strong hind limbs, with perfect webbing between the toes. The 

 eggs are laid in large masses. The following species inhabit the British 

 Isles: the Common or Grass Frog {Bana temporaria), which usually 

 lives on land, and betakes itself to the water only at the breeding season, the 

 early spring, in contradistinction to the large Edible Frog (JS. esculenta),. 

 which lives the whole year through in water, and which swims and springs better 

 than the others ; it spawns later also, and its larvae -attain a considerable size. 



2. Tree Frogs (Syla, etc.), are distinguished from others in having a 

 sucking-disc at the tip of each toe. The green Syla arborea, which is usually 

 found on trees, except during the breeding season, occui's over most of Eiirope. 



3. Land Frogs, or Frog-toads (PeZofeaiit?*) difPer from tme Frogs, 

 in the short hind legs ; erect pupil ; and wai-ty skin. The following European 

 forms may be noted : the Orange-speckled Toads {Bomhinator igneus 

 and B. homhinus), ventral surface black and yellow ; Pelobates fuscus, hind foot 

 with a homy knob, sharp as a knife on its inner side ; the larva reaches a still 

 greater size than that of the Edible Frog ; Alytes obstetricans. of which the males 

 wrap the eggs round their hind legs and carry them about with them until the 

 larvse are ready to hatch, when they go into the water and the lai-vse leave the 

 egg-shells. 



4. The Toads (Bufo) are edentulous, have shorter hind limbs than the 

 Frogs, and an imperfect web between the hind toes, transverse pupils, warty skin. 

 The eggs are laid in long strings. In England : the Common Toad 



