12 EMBRYOLOGY 



and egg arise from the cells of the adult. How is sex determined ? What is 

 the role of the genes in sperm and egg during development ? 



These problems, which have been briefly outlined, are being studied 

 today, and progress is being made. In what follows an attempt will be made 

 to discuss some of the progress made on some of these problems. From 

 these discussions we shall attempt to formulate the principles which will 

 guide us in the consideration of all problems in development. 



