194 



YVETTE W. KUNZ 



cardial folds extend to the end of the otic vesicles. Capillaries lie at the base of 

 the outer sheet of the pericardial folds; they are continuous with the vascular 

 network of the yolk sac (Fig. 6c, 7c). 



Stage 6 (15th embryonic day) 



a) Average length of embryo 5.1 mm. Eyes appear black. Yolk material 

 diminishes markedly and now only covers two thirds of the eyes. As the yolk 

 is gradually used, the lumen of the yolk sac is encroached upon by the enlarging 

 bilobed urinary bladder. Rays have made their appearance in pectoral and caudal 

 fins. Pectoral fins twitch at irregular intervais. The entire head is covered by a 

 vascular network, which is supplied by the anterior branches of the ductus Cuvieri 

 (Fig. 4c). 



a) stage 7 (20th e.day), b) stage 8 (25th-30th e.day) 



