TOADS AND FROGS. 63 



principal diet is the vegetable matter that grows on the stones 

 or weeds in its pond. Tadpoles are not above cannibalism 

 if driven to it by hunger. In ponds with meagre food supply 

 the ragged and frayed tails show where they had begun to eat 

 each other, and some individuals may entirely disappear. 



'The Balance of Nature.' — The vegetable growth in the water 

 not only supplies the tadpoles with food but, if it be green, with 

 oxygen also. The living green plants in daylight are con- 

 stantly giving off oxygen, which is absorbed by the water and 

 taken up by the gills of the young tads to purify their blood. 



3 4 



1, Nostril. 2, Mouth. 3, Ear. 4, Gill-cleft. 



The waste given off by their bodies is taken up as nourishment 

 by the plants ; each uses the other's waste, so between them 

 the house is kept quite clean. A tadpole seems to be little 

 else than head and tail, but it really has, as befits a vegetable 

 feeder, a long intestine coiled up like a watch-spring. 



Legs and Tail. — The next change that the pupils will be 

 able to observe will be a pair of little stumps near the junction 

 of the tail with the body. These will elongate and reveal 

 their character as hind legs. In the case of the frog, at the 

 age of two months, the toes can be made out. The smaller 

 front legs are growing at the same time, but they are hidden 

 under the fold of skin that covers the gills and are not seen 

 until they burst through it. Children are apt to think that 

 the front legs have grown suddenly. As the legs lengthen the 

 tail shortens ; it is gradually being absorbed. Other changes 

 are in progress, the mouth is flattening and lengthening ; in 

 some kinds teeth are developing in the roof of the mouth and 

 in the upper jaw. 



