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YVETTE W. KUNZ 



b) The whole lens (except for the surface epithelium) is now fibrillar and the 

 layers of the retina are évident (Fig. 6d). 



The histological sections show that the cavities of the pericardial folds are 

 not fused dorsally. The capillaries spread over the whole outer wall of the 



Fig. 7 



Diagrammatic représentation of sections shown in Fig. 6 



pericardial folds, but do not cross over from one side to the other; the dorsal 

 somatopleural bridge marks the line of division. The inner walls of the peri- 

 cardial folds, which are not vascular, adhère closeîy to the inner sheet of the ecto- 

 dermal headfold. The pericardial folds extend posteriorly to the pectoral fins 

 (Fig. 6d, 7d). 



Stage 7 (20th embryonic day) 



a) Length of the embryo averages 6.1 mm. Head elongates and yolk extends 

 only to the middle of eyes. Yolk material is almost used up and urinary bladder 



