Fig. 24. The fate of the gray crescent in normal development. Left: The 

 gray crescent is shown with a square of blue dye applied as a marker. Center: 

 In a later stage of development (gastrula) the gray crescent is no longer visible 

 but the marker persists and is found just above the dorsal lip. Right: With 

 further development of the gastrula into an embryo the blue marker can be 

 traced into the head endoderm. Therefore the normal fate of the gray crescent 

 protoplasm is to form head endoderm. 



ANTERIOR END 



EARLY GASTRULA 



Fig. 25. The fate of various regions of the gastrula 

 during development. Right: A simplified diagram of 

 the embryo at a stage when various structures can be 

 visibly identified. Abate: Outline of an early gastrula 

 with the dorsal lip as a point of orientation, a, b, c, 

 etc. are small groups of cells stained with dyes in 

 order to mark these regions and trace them into the 

 embryo. The same letters appear in the embryo and 

 mark the structures or regions derived from the corre- 

 sponding groups of cells in the gastrula. 



58 



OPENING OF GUT 



POSTERIOR ENO 



