380 



FISH FOR EXPERIMENTATION 



It seems apparent from the work of Morgan (1895), Lewis (1912), Hoadley (1928), Nicho- 

 las and Oppenheimer (1942) and Tung (1943) that the early blastodisc can adjust to the 

 removal of single or groups of blastomeres, and still give rise to normal embryos. This 

 suggests that there is no qualitative division in the early stages of Fundulus, and that all 

 regions are totipotent. It now appears that all parts of the trout blastula are equipotent 

 (Luther, 1937) and, when the blastoderm of the blastula stage is quartered, each gives 

 rise to tissues and organs (in tissue culture or transplantations) representing all parts of 

 the embryo. 



Gastrulation is the time when there is qualitative segregation of areas, and Oppenheimer 

 (1936) and Luther (1935) have shown that the dorsal lip of the blastopore functions in 

 teleosts much as it does in the amphibia. Secondary embryos can be induced by hetero- 

 topic transplantations of pieces of the dorsal lip. Oppenheimer (1947) believes that the 

 Fundulus dorsal lip shows regional determination, supported by the studies of Eakin 

 (1939) in Salmo. 



EPIBOLY OF FISH BLASTODERM 



EXPANSION OF BLASTODERM 



ANIMAL POLE 



VEGETAL POLE 



G.R. 



^ YOU< ^ ^^ ^ ^ 



ANIMAL POLE VIEW 

 GASTRULATION- APPEARANCE OF GERM RING 



EXTRA EMBRYONIC MEMBRANE 



C.N.S. 



G.R. 



SIDE VIEW YOLK PLUG 



DEVELOPMENT OF EMBRYONIC SHIELD AND EMBRYO 



(Redrawn from Oppenheimer 1936) 



