IX 



MOLLUSCA 



SS 



359 



stoni 



FIG. 290. Two sagittal sections of early embryos 

 of Loligo vulgaris in order to illustrate the 

 tirst formation of organs. (After Faussek.) 



A, Stage in which the endoderm is first visible as a 

 differentiation of the mesoderm. B, Stage in which the 

 ink sac is formed, end, endoderm ; i.s, ink sac ; mes, 

 mesoderm s.s, shell-sac ; stom, stomodaeum ; y.m, yolk- 

 membrane. 



en 



mes 



