248 EARLY STAGES OF ARTHROPOD AND VERTEBRATE EMBRYOS. 



parts of the so-called "archenteron" that can be justly regarded as endodermic are 

 the two lateral bands that in both vertebrates and arthropods actually form the 

 lining of a functional alimentary canal. (Fig. 270.) 



True gastrulation, comparable with the formation of an enteric chamber in 

 coelenterates, is a much less important process in arthropods and vertebrates than 

 has been supposed, and is confined to the central region of the procephalon. 



