EXPERIMENTAL FISH EMBRYOLOGY 



589 



FUNDULUS HETEROCLITUS 



I A B C D ] 



D"J» 



A"» 



^1122 A"2lB"*'B"" 



The typical cleavage pattern of the 

 egg of Fundulus heteroci itus . Schematic. 

 A represents the uncleaved blastoderm, B 

 the two-cell stage, C the four-cell stage, 

 D tlie eight-cell stage and E tlie sixteen- 

 stage. V and G show the direction of the 

 fifth and sixth planes of cleavage in the 

 marginal cells of the sixteen-cell stage; 

 these planes are not represented in tlie 

 central cells of the sixteen-cell stage 

 because they are here horizontal and dif- 

 ficult to follow. 



A, B, C, D and E are drawn at approxi- 

 mately the same scale; the magnification 

 is greater for F and G. The position of 

 the first four planes of cleavage is in- 

 dicated by niomerals; see text for explana- 

 tion of the designation of cells by letter 

 and number. 



Diagrams illustrating the results of ex- 

 periments in which stained blastomeres were 

 followed through to gastrulation. The 

 figures marked "A" in each case represen the 

 blastoderms immediately after staining those 

 marked "B" and "C" are the later stages of 

 the same embryos. 



The relation of the first or second 

 cleavage plane to the embryonic axis may be 

 determined. Occasionally the embryonic axis 

 is oblique to the early cleavage planes. 



Usually two of the 8-cell stage blas- 

 tomeres or four of the marginal cells of 

 the 160-cell stage blastoderm give rise to 

 the early embryonic shield, and (in one in- 

 stance) two of the 16-cell stage blastomeres 

 formed the entire shield. The germ ring is 

 formed by peripheral cells of the 32-cell 

 stage and the material for the fore-brain 

 comes from the central cells of the 16-cell 

 stage. 



From Oppenheimer 1956: Jour. Exp. Zool. 73:'*05) 



