The Develoi)meiit of the Heart in Shad. 215 



In order to identify the parts briefly described above with the 

 structures found in the adult, it may be said that during the rapid 

 dwindling of the yolk the piers of the arched supravitelline sinus ap- 

 proach each other and that between them, by a process of rearrange- 

 ment of vascular endothelium, there is formed a vein, the hepatic 

 vein of the adult. The portion of the heart-wall connecting the 

 venous end of the atrium with the parietal pericardium forms not 

 only the anterior wall of the sinus venosus, but also the pericardial 

 surface of the pericardio-peritoneal septum. The posterior wall of 

 the sinus venosus, together with the peritoneal surface of the 

 pericardio-peritoneal septum, is furnished by the anterior part of 

 the splanchnic peritoneum. 



Wo vitelline vessels, other than the hepatic vein (derived from the 

 vascular endothelium lining the roof of the supravitelline sinus) 

 are ever developed. 



Contrast drawn between embryos of the shad type and those in 

 which a vitelline vessel-networh occurs. Suggested classification of 

 teleostean embryos into moryhological types depending on the rela- 

 tion of the ventral vessel system to the yolk. 



The entire absence of a network of vessels on the ventral and 

 lateral surfaces of the yolk imparts to the egg of shad (and to other 

 eggs of the shad type) an appearance strikingly different from that 

 of the teleostean eggs (e. g., those of Salvelinus) which for some 

 time before hatching display a vitelline vessel-network filled with 

 corpuscles. The type of egg to which shad belongs may be called 

 Type 1 in contradistinction to the type in which a vitelline vessel- 

 network occurs, which may be called Type 2. 



Type 1 appears to be almost universal in pelagic eggs. Uran- 

 oscopus scaber^ is the only pelagic teleost of which I find it recorded 



'The following are some examples of pelagic eggs in which a vitelline 

 vessel-network is stated not to occur, or in which its absence has been inferred 

 from figures depicting well-advanced stages : Elacate canada, Gadus morrhua 

 (callarias), Chaetodiptenis faber, Scomberomorus maculatus (Ryder '82, '84, 

 and '87). 



Hemipterus americaniis, Temnodon saltator, Lophius piscatorius, Ctenolabrus 

 (Tautogalabrns) adspersus, Tautoga onitis, Pseudorhombus oblongatus, Motella 

 argentea (Agassiz and Whitman, '85). 



Labrax lupus, Serranus cabrilla, S. scriba. Sargus Rondeletii, Box vulgaris, 



