230 REPRODUCTION IN PLANTS AND ANIMALS 



directly into an adult. 



is a small oval object, usually green, but sometimes varying a 

 little to harmonize with its surroundings. This stage remains for 

 two weeks in summer and longer in cold weather. It then cracks 

 open down the back and the adult butterfly, or ima'go, comes out. 

 A complete metamorphosis is shown by this insect, which during 

 its development passes through four distinct stages — egg, larva, 

 pupa, and adult. Most insects show a complete metamorphosis. 

 Metamorphosis of the Frog. — Not all vertebrates develop 

 The frog, for example, undergoes a meta- 

 morphosis. Let us ex- 

 amine the development 

 of the common leopard 

 frog. 



The eggs of this frog 

 are laid in shallow water 

 in the early spring. 

 Masses of several hun- 

 dred, which may be 

 found attached to twigs 

 or other supports under 

 water, are deposited at 

 a single laying. Im- 

 mediately before leaving 

 the body of the female 

 they receive a coating 

 of jellylike material, 

 which swells up after the 

 eggs are laid. This helps 

 to protect them from 

 attacks of fish or other 

 animals which might use 

 them as food. The up- 

 per side of the egg is dark, the light-colored side being weighted down 

 with a supply of yolk (food) . The f ertihzed egg soon segments (di- 

 vides into many cells), and in a few days, if the weather is warm, it 

 has grown into an oblong body which shows the form of a tadpole. 

 Presently the tadpole wriggles out of the jellylike case and begins 

 life outside the egg. At first it remains attached to some water 



Metamorphosis of a frog. 1 to 7, much enlarged ; 

 4, 5, and 7, in section ; 8, tadpole with external gills ; 

 9 to 11, tadpole with internal gills. Notice the de- 

 velopment of the legs and the disappearance of 

 the tail. 



