256 



H. D. S( 



derm (compare Figs. 20 and 24). The shrinkage of the yolk has 

 had an effect on the shape of the future hepatic veins; the latter 

 are now semilunar rather than crescentic in section. The ventral 



position oF Fig. 25 

 position 0^ Fig. 24 

 position of Fig. 23 



Ectoderm 



Otocyst 



Left jugular vein 



L. cardinal v. 

 CEsophagus 



Posterior wall of 

 sinus venosus 



Ventral 

 aorta 



Arrow in L. hepatic vein 



(head of arrow rests on yolk) 



Left wall of 

 L. hepatic vein 



Parietal peritoneum [cut] 



Branchial a. 3' Conus 



Dorsal parietal pericardium 



Ectoderm 



Ventricle i 

 Atrium 

 Anterior wall ofy 

 sinus venosus ' 



Ventral parietal pericardium 

 (mostly removed) 



Fig. 22. — The left side of a recoustructiou from the posterior gill region 

 of shad, stage of 166 hours. X 100 diams. 



Sufficient body-wall has been removed to open the pericardial coelom laterally 

 and ventrally and the peritoneal ccelom laterally. The anterior pole of the 

 yolk is intact, the ventricle and atrium have been opened. The vein imme- 

 diately ventral to the left jugular is the left inferior jugular. 



part of the pericardial ccelom has extended backward, so that the 

 endocardium lining the anterior wall of the sinus venosus assists in 

 the formation of the hepatic veins (see Fig. 24). The expansion 



