FIG. IV. Ventral view, 32-34 hours. The lateral folds (LF) 

 have just made their appearance. 



FIG V. Ventral view. About 36 hours. The lateral folds 

 have greatly lengthened, and the lateral plates (LP) are ap- 

 proximating each other. The head fold of the amnion (Am) 

 and the anterior mesenteron rudiment (AMR) are now visible. 



FIG. VI. Ventral view. 38-42 hours. The lateral plates 

 (LP) have become united along the greater portion of their 

 length. The posterior mesenteron rudiment (PMR) is now 

 visible. 



