EXPERIMENTAL CHICK EMBRYOLOGY 



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1. Begression of the primitive streak, formation and elongation of the notochord. 



2. Formation and closing of the neural folds. 

 5. Development of the hrain and spinal cord. 

 k. Formation of somites. 



5. Development of optic vesicles and otocysts. 



6. Morphogenesis and pulsation of the heart. 



7. Formation and extension of a "tail" from the cut edge of the anterior piece. 

 He states: "A medium which meets all of these requirements is considered adequate." 



From the works of 'Spratt it seems evident that the early tlastoderm does not have 

 adequate endogenous food supply (as does the fish emhryo) hut depends upon some exogenous 

 source for nutrition. The best medium proved to he the entire egg (yolk and albumen) ex- 

 tracted and added to a saline-agar base. The albumen seema not only to be bacteriolytic 

 but also seems to help maintain the proper pH of the blastodermic environment. A "com- 

 plete" synthetic medium was finally devised, containing saline-agar, glucose, amino acids, 

 vitamins, etc. on which explants xinderwent essentially normal morphogenesis, differentia- 

 tion, and some growth. However, Spratt subsequently found that the glucose component was 

 the only absolutely essential exogenous source of energy for morphogenesis and differen- 

 tiation of the explanted early blastoderm. These developmental processes occurred in the 

 almost total absence of growth. Mannose, fructose, and maltose were apparently Just as 

 efficient as was glucose. 



In a study by Rawles (I956) followed by Eudnlck (1958) it has been possible, by ex- 

 plantation and chorio-allantoic grafting, to map the organ forming areas of the early chick 

 blastoderm. Eawles found that the developmental potencies within each area diminish 

 peripherally from the center, and that there is superior developmental capacity of the 

 left side of the blastoderm over the right. 



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REGIONS OF ORGAN ANLAGE IN EARLY CHICK BLASTODERM 



This chart is made from the combined data of Willier and Bawles. 



