100 THE ANIMALS AND MAN 



a small stone covered with the growth of microscopic plants, 

 and some water should be taken from the pond to the arti- 

 ficial pond. The water will supply the place of that which 

 has evaporated, and the mud and stones will carry a new 

 supply of feed." 



The tadpoles will begin to change very soon. Make a 

 drawing of one just hatched from the egg, examining it 

 with a hand lens. Note the gills on the sides of the neck, 

 the V-shaped sucker on the head, and the absence of legs 

 and eyes. Watch sharply for the first changes. What are 

 they? 



It takes a tadpole about two months from the time of 

 hatching to complete its development and hop out of the 

 water as a httle toad or frog. In this process of develop- 

 ment the following changes occur: eyes appear; the gills are 

 lost; four legs develop; the tail is gradually lost, and lungs 

 are formed inside the body. The development of the lungs 

 cannot be actually seen, but its course is made apparent by 

 the behavior of the tadpoles. While at first they remain 

 under the water nearly all the time, breathing by means 

 of their gills the air dissolved in the water, as they grow 

 older they come more and more often to the surface and gulp 

 down air through the mouth. Lungs are developing, and 

 are being more and more used for breathing air from the 

 limitless supply above. 



Observe carefully the process of the disappearance of 

 the tail. Does it drop off suddenly? Is it lost before the 

 legs develop? Which pair of legs appears first? The order 

 of their appearance differs in the toad tadpoles and the frog 

 tadpoles; if both kinds are being reared determine this by 

 observation. 



Make a drawing of a tadpole just after its legs appear, 

 and compare with the drawing of the newly hatched tadpole; 

 make also a drawing of a little toad or frog when it first 

 finishes the tailed tadpole stage and hops out of the water. 



