832 BULLETIN OF THE BUREAU OF FISHERIES 
slightly heavier than fresh water and sink to the bottom of unagitated water. How- 
ever, a slight movement of the water serves to float the eggs and keep them in suspen- 
sion. The egg membrane, or chorion, appears heavily corrugated and nearly opaque 
after preservation. Living eggs show a transparent chorion at all times. The yolk 
sphere is heavily granulated, about 1.10 mm in diameter, of a rather intense green 
color in live eggs, and usually of a pale amber color in preserved eggs. It contains 
an amber-colored oil globule that measures 0.56 mm in diameter. Several much 
smaller oil globules may also be present. (See fig. 3.) 
The egg at 15 minutes after fertilization increases by the rapid absorption of 
water to about 1.84 mm in diameter. The size of the yolk sphere and the oil globule 
remains the same during the early developmental stages. The blastodisc appears 
differentiated at one end. of the yolk sphere. The chorion, becoming stretched, is less 
corrugated. It was noted by Scofield and Coleman (1907) that the first cleavage of 
the germinal disc takes place about 2 hours after fertilization. (See fig. 4.) 
The egg at 12 hours after fertilization shows a considerable increase in size. 
The egg diameter may range from 3. 2-3. 8 mm and water absorption appears complete. 
The chorion is thin, transparent, and fragile. The blastoderm is in late cleavage and 
the periblast appears clearly differentiated about the yolk sphere and becomes a paler 
green with age. (See fig. 5.) 
The egg at 24 hours after fertilization shows no further expansion of the chorion. 
The embryo becomes differentiated and extends about half way around the circumfer- 
ence of the yolk. A moderately intense pigmentation of the embryo occurs and 
consists of small black dots distributed over the dorsal aspect of the body and over a 
part of the adjacent blastoderm. (See fig. 6.) 
The egg at 36 hours after fertilization has an embryo about 1.6 mm in length. 
Eyes become differentiated but lack pigmentation. The posterior part of the embryo 
body is free from the yolksac. (See fig. 7.) 
The egg at 48 hours after fertilization, kept at a temperature averaging 64.2° F., 
is about to hatch. The embryo is approximately 2.5 mm in length upon leaving the 
egg. (See fig. 8.) 
The larva at 60 hours after fertilization of the egg measures about 3.2 mm in 
length. The oil globule, embedded in the anterior end of the yolksac, projects 
beyond the head of the larva. The newly hatched fish tends to settle to the bottom 
of a still aquarium despite swimming efforts to remain near the surface. A strong 
current of water, however, enables the fish to keep suspended and in more or less 
constant motion. Hatchery fish are usually liberated soon after this stage. (See 
fig. 9.) 
The larval fish at 84 hours after fertilization of the egg increases to about 4.4 
mm in length. The head projects beyond the oil globule. A series of small chroma- 
tophores appears along the ventral surface of the body posterior to the vent but the 
eyes continue to lack pigmentation. (See fig. 10.) 
The larva at 120 hours after fertilization of the egg measures 5.2 mm in length. 
The eyes now possess pigmentation and the jaws are somewhat developed. The oil 
globule and yolksac are considerably reduced as the rudiments of the digestive tract 
appear. The pectoral fin s become differentiated. The ventral chromatophores 
become somewhat stronger and several of them now lie along the edges of the gut. 
(See fig. 11.) 
