30 FIRST LESSONS IN ZOOLOGY 



" One must not attempt to raise too many tadpoles in 

 the artificial pond or there will not be enough food, and 

 all will be half-starved. While there may be thousands 

 of tadpoles in a natural pond, it will be readily seen that, 

 compared with the amount of water present, there are 

 really rather few. 



" Every week, or oftener, a little of the mud, and per- 

 haps a small stone covered with the growth of microscopic 

 plants, and some water should be taken from the pond to 

 the artificial 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 little 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. 



( )bservc carefull)' the process of the tHsa|ipearance of 

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

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



