The Development of the Heart in Shad. 



253 



ward from the anterior wall of the sinus venosus to a projection 

 on the yolk (dorsal to the anterior pole of the latter) forms an 



position of Fig. 21 

 position of Fig. 20 I 

 position of Fig. 19 

 position of Fig 



Otocyst 



Spinal cord 



Ectoderm 



-Notochord 



Dorsal aorta 



Peritoneal coelom 



L. cardinal v. 



CEsophagus 



R. cardinal v. 



Supravitelline sinus 



L jugular v. 



Br. cleft 2 

 Branchial cleft 3' 

 Branchial a 4 

 Branchial a. 3 

 Ventral aorta 



Dorsal parietal pericardium 



Conus arteriosus 

 Atrium 

 Anterior wall of sinus venosus 



Ventral parietal pericardium 



(mostly removed) 



Fig. 17. — The left" side of a reconstruction from tlie posterior gill region 

 ot a sliad, stage of 114 hours. X 100 diams. 



Exphination as in Fig. 1. Notk. — The warping of the posterior phites of 

 this reconstruction (concavity forwards) was not noticed before drawing; 

 otherwise it would have been rectified. The wai-ping has to be taken into 

 consideration in estimating the correct positions of Figs. IS, 19 and 20. 



incomplete septum between the right and left sides of the sinus 

 venosus. The two sides of the sinus venosus are in communica- 



