26 INTRODUCTION TO THE EMBRYOLOGY OF THE LEOPARD FROG 



3. Early cleavage 



4. Blastula stage — coeloblastula (see Glossary) with eccentric blastocoel 



5. Gastrulation 



Early — crescent-shaped dorsal Up 

 Middle — semi-circular blastoporal lip 

 Late — circular blastoporal lip 



6. Neurulation 



Early — medullary plate 



Middle — neural folds converging 



Late — neural tube formed and ciliation of embryo 



7. Tail bud stage — early organogeny 



8. Muscular response to tactile stimulation 



9. Early heart beat, development of gill buds 



10. Hatching and gill circulation 



1 1 . Mouth opens and cornea becomes transparent 



12. Tail fin circulation established 



13. Degeneration of external gills, formation of operculum, development of 



embryonic teeth 



14. Opercular fold over branchial chamber except for spiracle; internal gills 



15. Prolonged larval stage with refinement of organs 



16. Development of hindlimbs, internal development of forelimbs in oper- 



cular cavity 



17. Projection of forelimbs through operculum, left side first 



18. Absorption of the tail and reduction in size of the gut 



19. Metamorphosis complete, emergence from water as miniature, air- 



breathing frog 



The rate of development of the egg and embryo will depend upon 

 the temperature at which they are kept. The approximate schedule of 

 development at two different temperatures is given below. 



Stage At 18 



Fertilization 



Gray crescent 1 



Rotation li/^ 



Two cells 3V2 



Four cells 4V2 



Eight cells 5V^ 



Blastula 18 



Gastrula 34 



Yolk plug 42 



Neural plate 50 



Neural folds 62 



Ciliary movement 67 



Neural tube 72 



Tail bud 84 



