596 
BULLETIN OF THE BUREAU OF FISHERIES 
described stage (72 hours), and shows greater activity. The tail appears to be quite 
free and the eyes, which are very prominent, frequently are “rolled” within their 
sockets. Circulation is very brisk, corpuscles now being plainly evident in the blood. 
The aorta can be seen to turn on itself in the tail of the embryo in those specimens 
that happen to be in such a position that a lateral view is obtainable. Several blood 
vessels are now visible in the yolk. Some golden color markings without definite 
outlines have appeared on the head of the embryo in some of the eggs and mixed with 
the golden color are two dark chromatophores. The yolk which has become greatly 
reduced and somewhat half-moon shaped usually is marked with several large irreg- 
ularly shaped dark spots or blotches. Much variation in the size, shape, and number 
of these spots exists among specimens. One specimen, for example, had a single large 
elongate black blotch, whereas others had many smaller spots. A few specimens 
were seen in which a few yellow spheres remained in the yolk. The egg remains round, 
as seen from above in its attached position, and according to measurements made of 
four eggs no measurable change in the diameter has occurred (fig. 101). 
Hatching begins during the sixth or 
seventh day after fertilization when a tem- 
perature of about 26° to 28° C. prevails, 
and it may extend over a period of at least 
24 hours. That is, among a batch of eggs 
all fertilized at the same time, some of the 
eggs may hatch fully a day earlier than 
others. An incubation period of 6 to 8 days 
at the comparatively high temperature 
which pervaded during the present study is 
regarded as a very long one for such a 
small egg. Many other marine fish eggs 
of simdar size which have been studied 
hatched in 2 to 3 days. 
Just before hatching, the eggs become 
somewhat distorted, that is, the portion of 
the egg case at the head of the embryo 
protrudes, causing the egg to become elon- 
gate and to have a somewhat uneven out- 
line. The egg and embryo are more opaque than previously and the structures are 
even more difficult to see. On the head of the embryo is a network of yellow and 
black markings, and at midbody length are dark, more or less branched, cross lines. 
The embryo is capable of much movement and appears to struggle, probably in an 
effort to break the egg case. 
Newly hatched fish .- — The newly hatched fish is close to 2.4 mm long. It emerges 
with an extremely small yolksac. Although the fish is very stocky anteriorly its 
tail is long and rather slender; preanal length is contained 2.45, and postanal length 
1.7 times in total length without the caudal fin membrane. The head is blunt, the 
mouth large and slightly inferior, and the pectoral finfold is prominent. The eye is 
relatively large, much longer than the snout, and nearly half the length of the head. 
About 26 myomeres are present. The body is quite transparent and the outline 
of the brain, the heart, and the circulation can be seen rather plainly. 
The head and trunk are largely overcast with a yellowish tinge; two irregular 
dark spots (or simply a blotch in some specimens) are present below the auditory 
vesicle; a large dark area is present on the upper part of the abdominal mass; and 
Figure 101. — Hypleurochilus geminatus. From egg with 
large embryo: 4 days after fertilization. H, heart; BV, 
blood vessels. Arrows indieato direction of flow of blood. 
