FROGS AND TOADS 259 



or respiratory pore, on the left side of the throat (compare with 

 fishes). 



4. The mouth in this stage is a small opening, furnished with horny 

 teeth and horny sheaths on the jaws. The food of the larva now 

 consists chiefly of dead vegetable substances. With the scum of algae, 

 etc., which covers stones and the larger aquatic plants, the larvae also 

 take up a quantity of microscopic animals, and are also fond of nibbling 

 at dead animals. The intestine is long and spirally coiled, enabling the 

 animal to take in and to thoroughly use up a large quantity of these 

 materials, which contain but little nutriment. (Compare the long 

 intestine of ruminants.) 



5. As the larva grows in size it undergoes a number of other changes. 

 First the hind-limbs and subsequently the fore-limbs are budded forth, the 

 skeleton becomes harder, and the swimming-tail gradually disappears. 

 The creature thus gradually becomes adapted for motion on land. 



The branchiae disappear, lungs being developed in their place ; thus 

 the animal becomes an " air-breather." The head assumes more the 

 frog-like shape, the mouth steadily increases in width, and the horny 

 teeth and sheaths are lost. The intestine assumes the shape typical of 

 carnivorous animals (see cat), the tongue is developed, and the animal 

 now begins to feed on living prey. In short, the fishlike tadpole has 

 become a frog. 



Other Batrachians. 



The commonest of our species of frogs is the Common Frog (Rana 

 temporaria; see illustration, p. 238). This animal is easily recognisable 

 by the dark spot in the region of the ear and the transversely striped 

 hind-legs. It changes its colour in accordance with its habitat, being 

 dusky grey or blackish-brown in woods where the soil is covered with 

 leaves, or similar localities, whilst on rich grassy tracts it assumes a 

 dress of lighter colours intermixed with green. It spawns as early as 

 March, and the larvae have reached their full development by June. 

 Hence this species can inhabit localities where the summer is only of a 

 few months' duration (Northern Europe, high mountains). The spawn 

 soon rises from the bottom. to the surface of the water, being thus 

 exposed to the direct rays of the sun — an advantage during the raw 

 season of the year — while the eggs are black, and thus absorb much 

 more heat from the sun than the lighter-coloured eggs of its green- 

 coated relative. (Dark clothes are warmer in summer than light clothes ; 

 why ?) The young frogs often leave the water in great swarms (popular 

 stories of showers of frogs), and disperse over gardens, meadows, 

 fields, and woods. During the daytime the frog generally secludes itself 



