CTENOPHORE 



TURBELLARIAN 



1 mes 



ECHINODERM 



ASCIDIAN I 



end 



ASCIDIAN II 



ANNE1ID 







proto. 1 



1 \ 

 1 1 . 1 



en<T^ 





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. 



