12 HJALMAR THÉEL, XOTES OX TITE DEVELOPMEXT OF ECHINOCARDIUM AXD PARECHIXUS. 



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Sectiona fcbrough fche ootodermio invagination the primarj amniotie oavitj and the hydroooelo hoop, everj 

 othei ection having been drawnj highlj magnified. a., primary amniotio oavity; e, eotoderm of the plutoua; ed., 

 dermic diaoj b., hydroooele hoopj Ipo., lefl poaterior coelom; si., stomach. 





