636 
BULLETIN OF THE BUREAU OF FISHERIES 
Larvae 16 hours old, 2.2 to 2.4- mm long . — In about 16 hours the yolksac is nearly 
all absorbed. The very small amount remaining is crowded with oil globules. The 
fish is now about 2.2 to 2.4 mm long. The head no longer is deflexed, but is rather 
elevated, with the hump even more prominent than in the newly hatched fish. The 
mouth is open, and the pectoral finfold on each side is plainly visible. 
It is interesting that, although pectoral finfolds are present in the larvae, pectoral 
fins are not developed. At least, not a rudiment of a pectoral fin was found in 186 
adults, collected at various places along the Atlantic and Gulf coasts of the United 
States, especially examined for this character (fig. 152). 
Larvae 24 hours old .— In the aquarium the fish did not increase much, if any, in 
length for several days after the yolk was absorbed. The fish shown in figure 153 
was only 2.18 mm long at 2 days of age, and therefore a little shorter than the younger 
fish shown in figure 152. Development, nevertheless, progressed somewhat. The 
yolksac with its oil globules had entirely disappeared. In its place there was a body 
wall through which the internal organs in part were visible. The hump on the head 
had become rather lower, and the mouth had moved forward somewhat with the lower 
jaw projecting slightly. The general color remained about the same as in the younger 
larvae. However, the pigment areas in the finfolds had become smaller and the 
pigment dots more concentrated (fig. 153). 
Larvae 4 days old . — Four days after hatching the larvae still did not exceed a 
length of 2.5 mm. The head now had become more elongate, and the mouth more 
prominent with the lower jaw projecting rather strongly. The body had remained 
slender, as in the younger larvae. 
The critical stage in the fife of the larvae seems to be reached about the fourth 
day, and few survived until the fifth in the glass dishes in which they were kept in the 
laboratory. However, among those fed with towings, of which mention already has 
