Snakes and Frogs and Their Relatives [225 



the following summer; bullfrogs may remain in a tadpole state 

 for two or three years! 



How THE EGGS DEVELOP 



We find frog eggs laid in a transparent protective jelly. 

 The shape of the jelly mass is one clue to the species; the date 

 it is discovered is another. The eggs of leopard or wood frogs, 

 for example, may be found by the first of April; those of the 

 green frog do not appear until a bit later, and the bullfrog may 

 not lay before July. The leopard frog's egg masses are in the form 

 of a flattened sphere; those of the wood frog are round masses. 



In the earliest stages, as the original single cell gradually divides 

 into many, you can follow the egg's development only with the 

 aid of a magnifying glass. It is only when the embryo begins to 

 lengthen that it can be easily seen with the naked eye. After five 

 or six days the embryo has a tadpole form, but it is still inside 

 the jelly mass. About the ninth day the tadpole breaks loose from 

 its protective covering. 



How A TADPOLE GROWS 



The Development of the Head: At first the tadpole is so shapeless 

 that the only way to know head from tail is to observe the direc- 

 tion in which it swims the head naturally goes first. But soon 

 the head grows larger. Instead of a mouth the tadpole has a V- 

 shaped raised sucker by which it attaches itself to water weeds. 

 Later this gives way to a small round mouth provided with horny 

 jaws. As the tadpole grows, the mouth gets wider and larger. 



How the Tadpole Breathes: When you observe the tadpole you 

 see little tassel-like gills appear on either side of the throat. 

 Blood passing through the gills is purified by coming in contact 

 with the oxygen in the water. Later the feathery gills disappear 

 as a membrane grows down over them, and they function inside 

 the body instead of externally. Water taken in through the nostrils 

 passes through an opening in the throat, on over the gills, and 

 out through a little opening, or breathing pore, at the left side 

 of the body. This breathing pore may easily be seen in larger 

 tadpoles. 



