CTENOPHORE 



TURBELLARIAN 



ASCIDIAN II 



FIG. 43. TYPES OF EGG ORGANIZATION IN DIFFERENT PHYLA; 

 cross-hatched area, mesoderm or mesenchyme (mes) ; hori- 

 zontal lines, endoderm (end); clear area, ectoderm (ect). In 

 the first four figures the pattern of localization is that which 

 is found at the close of the first cleavage; in Ascidian II the 

 pattern is that which is found at the close of the second 

 cleavage; in the annelid egg the localization of later stages is 

 projected upon the egg; n.p., neural plate; ch., chorda; 

 e.g., cerebral ganglion; v.g., ventral ganglion; proto., 

 prototroch. 





