no en- 

 are 



Plate IV. Development of 

 the gopher frog, Rana aesopus. 

 I. Egg mass (xf). i. Eggs 

 (X|). 3-7- Tadpoles (x|). 

 (4. Lateral lines and spiracle; 

 5. two legs; 6. three legs; 

 7. four legs.) 8. Transformed 

 frog(xf).9. Adult (Xi). 



Development and transfor- 

 mation. Some frogs have lim- 

 ited breeding periods and 

 other species may breed al- 

 most any month in the year. 

 The males usually precede 

 the females to the water and 

 croak vigorously during 

 breeding time. The male 

 with its forearms seizes the 

 female. In almost all frogs 

 the eggs are fertilized just at 

 or slightly after the extrusion 

 of the eggs. At first 

 velopes about the eggs 

 apparent and the egg mass 

 may feel soft and sticky. 

 After a few minutes this sub- 

 stance absorbs water and 

 each egg is then revealed 

 with its vitelline membrane 

 and one or more jelly en- 

 velopes. 



The eggs hatch in 3 to 25 

 days, depending on tempera- 

 ture and other conditions. 

 At hatching, the larva has a 

 distinct neck, with a promi- 

 nent head and body. The 

 tail is very small or absent. 

 \ ^ . ^ On the ventral side of the 



JtiL % * ||f head is an invagination or de- 

 / ( .^^rW^ pression which is to be the 



7 * mouth. Behind this comes 



the ventral adhesive disk or 

 disks, which help the little creature to attach itself to the egg mass or to 

 hang itself upon some plant. In front of the mouth are two deep, dark 



II 



