Male and Female 25 



ovary. But the process may be followed with 

 ease in the case of the frog's egg or the toad's 

 egg, easily obtained in spring. The eggs of 

 these animals are formed in the ovaries during 

 the fall and winter months. They are dis- 

 charged by the female frogs in masses almost 

 as soon as the ice is gone from the ponds and 

 in strings by the toad about a mqnth later. 

 When discharged they are spherical bodies as 

 large as the head of an ordinary pin, black on 

 one side and white on the other. As they lie 

 in pond or stream the black side is uppermost. 

 The female lays her eggs early in the 

 morning, and at the same time the male dis- 

 charges into the water the sperm produced by 

 glands called the testes. Each sperm is a single 

 living cell with a vibratile tail by which it swims 

 to the egg. The sperms are so small they can 

 only be seen under the microscope. A sperm 

 unites with an egg after the same manner as the 

 fleck of living substance from the pollen grain 

 combines with the substance of the egg, and it is 

 only when this fertilization is accomplished that 

 the egg proceeds to grow into the little tadpole. 



