PLATE o 



EXPLAXATION OF FIGURES 



23 Section through the posterior heart -region of nieroplast Type II, no. 133. 



24 Transverse section of meroplast Type II, no. 96. The unilateral heart of 

 this embryo communicates with extraembryonic vessels. The aortic anlagen 

 are discontinuous. 



25 Transverse section through the trunk of meroplast Type II, no. 110, 

 showing a beginning of splanchnopleural concrescence. 



26 Section more anterior in same meroplast showing apposition of concres- 

 cing entoderm to close off the pharynx. 



ABBREVIATIONS 



AorL, aorta 

 Coel., coelom 

 EcL, ectoderm 

 Endc, endocardium 

 Endth., endothelium 

 Ent., entoderm 



Myc, myocardium 



Ot. ep., otic epithelimn 



Par. mes., parietal mesoderm 



Ph. pharynx 



Vis. mes., visceral mesoderm 



140 



