PLATE 12 



EXPLANATION OF FIGURES 



45 Section through the anterior heart region of the same meroplast show- 

 ing an entodermal proliferation of prevascuhir mesoderm 



46 Section between the planes of figures 44 and 45 showing a connection of 

 endothelium with entoderm. 



47 Section through the posterior heart region of the same meroplast show- 

 ing endothelium connected with entoderm. 



48 Section posterior to the plane of figure showing the prevascular tissue 

 in connection both with entoderm and with mesoderm. The connections with 

 the latter are not mere coagulations of a clear plasma, but are composed of a 

 real intercellular matrix. 



ABBREVIATIONS 



Endth., endothelium Ent., entoderm 



Pv. mch., prevascular mesenchyme 



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