1 1 EMBRYOLOGY 



the major structures of the adult. The foregoing analysis, however, has not 

 given us a complete picture of the development of any one organism. We 

 have used sea urchin, frog, salamander, and chick embryo indiscriminately in 

 order to bring to light the principles of development. At this time we propose 

 to describe the development of the frog egg in order to present a unified 

 picture in one species. With the principles clearly understood, the progressive 

 changes in development may be better understood. 



