SIXTY-TWO SPECIES OF FISHES FHOM LAKE ERIE 
311 
DESCRIPTION 
Egg . — Diameter after preservation in formalin mostly 2.8 to 3.0 millimeters; 
perfectly spherical, yolk yellowish or amber with half its surface covered by varying 
sized oil globules closely crowded together. Immediately after fertilization yolk 
entirely fills egg, with no perivitelline space apparent except at one pole. At 6 hours 
average diameter, 3.0; yolk diameter, 2.6 millimeters, with widened perivitelline 
space and the first concentration of germinal matter to form the blastodisc at center 
of oil globule mass. Blastodisc continues to form until the beginning of cleavage at 
24 hours, when 2, 4, and 8 cell stages are apparent. Blastodisc lenticular by fifth 
day with oil globules congregated below. On twenty-sixth day an early embryo 
reaches halfway around egg and shows well developed optic vesicles which are slightly 
pigmented on inner and upper margins. Oil globules coalescing in part to form 
usually about two very large spheres, with many small ones remaining. At 40 days 
the embryo extends completely around egg; head much higher and more rounded, 
eyes larger and black; 1 large oil globule and only a few smaller ones on yolk. First 
evidence of dorsal and ventral marginal pigmentation evident at 54 days. 
Figure 10 shows the embryo in process of hatching on the sixty-first day. Mouth 
not open; vent at a distance from body, at edge of fin fold; embryonic marginal 
fin fold completely encircling fish from behind head around lophocercal tail to yolk 
sac; yolk sac very large, deep yellowish in color, with 1 large oil globule and other 
smaller ones. Myomeres completely formed. Double series of brown chromato- 
phores on both dorsal and ventral aspects; yolk sac also pigmented posteriorly, near 
the body. Other eggs in collection not hatched at 131 days. 
12 .0-millimeter stage . — Less than 1 week old. Total length, 12.0; length to vent, 
7.0; greatest depth behind yolk sac, 1.1 ; diameter of eye, 0.8 millimeter. Body much 
heavier, the greatest depth behind yolk sac being 10.9 in total length, while in a herring 
of equal development it is 12. Embryonic marginal fin fold resemb ling herring, 
originating over middle of yolk sac, notching somewhat about 11 myomeres before 
