THE DEVELOPMENT OF THE HEART IN SHAD 



(Alosa Sapadissima, Wilson). 



With a Note on the Classification of Teleostean Embryos 

 FKOM A Morphological Standpoint. 



H. D. SENIOR. 



(From The Wistar In/ttitute of Anatomy and Biology, Philadelphia, and the 



Department of Anatomy in the College of Medicine, Syracuse University). 



With 27 Figures. 



CONTENTS. 



PAOE. 



Introduction — A brief description of the heart and great venous chan- 

 nels of a recently hatched shad 212 



Contrast drawn between embryos of the shad type and those in 

 which a vitelline vessel-network occurs. Suggested classifica- 

 tion of teleostean embryos into morphological types depending 



on the relation of the ventral vessel system to the yolk 215 



Statement of the object in investigating the development of the heart 



in shad, and of the scope of this investigation 219 



Material and Methods 219 



Development of the Heart 222 



Period 1. Formation of the heart anlage 222 



Review of the evidence bearing on the relation of the endo- 

 cardium to the vascular endothelium of the head in gen- 

 eral 232 



Period 2. Lasting until rhythmical contraction begins in the par- 

 tially formed heart-tube 237 



Period 3. In which the heart-tube is completed, to form conus, 

 ventricle, and atrium ; and assumes the adult position. 



Stage of G.2 nmi 249 



Correlation of the stages estimated by the number of somites 



with those designated by the length of the embryo 244 



Mechanism of the circulation in diffei'ent stages of develop- 

 ment 244 



Stage of C).2 mm 246 



Stage of 7.3 mm 249 



Stage of 8.75 mm., and a comparison of the heart with that of the 



stage described in the introduction 250 



Period 4. Formation of the sinus venosus and hepatic vein 252 



The American Jouunal of Anatomy. — Vol. IX, No. 2. 



