Gastmlation in the Pigeon's Egg. 



89 



rior to the dorsal lip the entoderm is almost wanting (Fig. 67). 

 In an uninjured blastoderm at a corresponding stage of development 

 the entoderm in this region is very thick (see Fig. 37). It is clear 



therefore, that while such an operation destroys most of the cells 

 that are to give rise to the entoderm, ^^ct the posterior margin is 

 still capable of forming a rounded dorsal lip. 



