98 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Figure 8. — Circa 1-1-hour stage with blastodermal cap. 



Figure 9. — Sixteen-hour stage with embryonic shield. 



visible about the time of blastopore closure. 

 Artificially fertilized eggs were not sampled at 

 this stage. Eggs estimated at the 24- and 30-hour 

 stages were obtained from plankton collections 

 made during the rearing studies. Particles adhered 

 to the suiface of artificially reared eggs, probably 

 due to the absence of water movement in the 

 culture bowls. Eggs from tlie plankton were 

 clean by comparison. 



The early-stage eggs showed little pigmenta- 

 tion. A few small cln-onuitopiiores were scattered 

 over the surface of the yolk, but none was appar- 

 ent on the blastula or early neurula. 



Figure 10. — Circa 24-hour stage from plankton with 

 early neurula. 



Figure 11. — Circa 30-hour stage from plankton with late 

 neurula. 



MIDDLE-STAGE EGG 



The developing embryo encircled two-thirds of 

 the yolk. Myomeres were visible along most of 

 the embryo, the head was well-defined, and the 

 optic lobes appeared as lateral expansions (fig. 11). 

 The late neurula was raised above the yolk as a 

 cylindrical embryo and not as a mere thickening 

 of the embryonic shield (fig. 12). At the end of 

 this stage, the tail had become separated from the 

 yolk and was curved laterally away from the 

 embryonic axis (fig. 13). This occurred 40 liours 

 after f(>rtilization. Small chromatopliorcs devel- 

 oped on the yolk, and several appeared along the 

 embryo, usually just posterior to the head. 



