The Development of the Heart in Shad. 



241 



heart anlage is of assistance in the folding over of the splanchnic 

 mesoderm to form a tube ; that it is not essential to this process is 



Head-fold ectoderm 



nc- 



Pharynx, ventral wall ny""' Lateral plate 

 chord '^ 



(closing) 



lie 



Fig. 11. — Venti-al surface of a recoustruction of the pericardial region of 

 shad, stage of 36 somites x 1^*0 diains. 



The heart-tube is in process of formation, contact of the two sides has 

 occurred along the broken line. The continuous black line encloses the area 

 covered by endocardium. Fixation by Pereny's method. 



indicated by the fact that a stage of 35 somites (half an hour 

 earlier) the folding over has already commenced, although it is not 

 so advanced as at 36 somites. 



