PLATE 11 



EXPLANATION OF FIGURES 



43 Section much anterior to the plane of figure 42, showing a double endo- 

 thelial tube surrounded by myocardium. This endothelium can be traced back 

 ■continuously to solid tissue the base of which is shown in figure 40. 



44 Transverse section of the middle heart region of meroplast Type II, no. 

 48. 



ABBREVIATIONS 



Endc, endocardium Myc, myocardium 



Endth., endothelium Par. mes., parietal mesoderm 



Ent., entoderm Vis. mes., visceral mesoderm 



152 



