FROG: EXTERNAL FEATURES AND BODY-WALL 23 



mass of spawn and fertilised by the sperm which the male 

 sheds over them as they pass out of the female. In about 

 a fortnight there hatches from each egg a little, fish-like 

 tadpole. This has no limbs, but a strong tail, which it uses 

 for swimming, breathes wholly by gills, and is at first with- 

 out a mouth. In a few days a mouth appears and the 

 animal begins to feed on vegetable matter. Gradually it 

 changes, losing its gills and tail and gaining lungs and two 



Fig. 7.— The Common Frog. 



pairs of limbs, till at the end of three months it becomes 

 a small frog. Henceforward it lives principally on land, 

 sometimes crawling about by means of both pairs of limbs, 

 but generally jumping with the strong hinder pair and 

 using the small fore pair to break its fall when it alights. 

 When it is frightened, however, it occasionally takes to the 

 water, and then swims strongly with its hind limbs. Its food, 

 after it has left the water, consists of slugs, snails, insects, 

 worms, and other small animals, the smaller prey being 

 caught by a sticky tongue, the larger seized with the mouth. 



