INTRODUCTION TO THE EMBRYOLOGY OF THE LEOPARD FROG 1 9 



terval between the annual spring breeding seasons. Breeding occurs 

 normally between the first of April and the latter part of May, 

 depending upon the latitude and upon variations in the tempera- 

 ture. Therefore Rana pipiens breeds for about two months, as the 

 temperature rises, from Texas to Canada. In any case, breeding gen- 

 erally occurs before the frogs have had an adequate opportunity to 

 secure food. This means that they must call upon what reserves of fat 

 and glycogen they did not consume during the extended period of 

 hibernation. The interval from egg-laying to metamorphosis of the 

 tadpole is about 75 to 90 days, this phase of development being com- 

 pleted well before the next hibernation period. 



Eggs generally are shed early in the morning, and Rana pipiens will 

 lay from 2,000 to 3,000 of them. The bullfrog, Rana catesbiana, has 

 been known to lay as many as 20,000 eggs. These are laid in heavy 

 vegetation to which their jelly coverings make them adherent. Eggs 

 are found usually in shady places, floating near the surface in rather 

 shallow water. 



Fertilization takes place during amplexus, the term for sexual em- 

 brace of female by male, as the eggs are laid (oviposition) by the 

 female. The cleavage rate depends upon the temperature of the en- 

 vironment and there may be a lag of from IVi to 12 hours between 



Animal hemisphere 



Gray crescent 



Vegetal 



hemisphere 



Stoge 2. 1 hr post- 

 fertilization. Right 

 side view. 



Stage 3. First cleavage Stage 4. Second Stage 5. Third 

 at 3.5 hrs. Posterior cleavage at 4.5 hrs. cleavage at 5.4 

 view. Right side view. hrs. 8 cells. 



Stage 7. Fifth cleavage. 

 32 cells at 7 hrs. 



Stage 10. Earliest 

 involution of dorsal 

 lip of 26 hrs. Pos - 

 terior view. 



Stage II Extension 

 of dorsal to lateral 

 lips at 34 hrs. 

 Posterior view. 



Stage 12 Complete 

 lip involution, en- 

 circling yolk at 

 42 hrs. 



Early development of the frog's egg. 



