436 
BULLETIN OF THE BUREAU OF FISHERIES 
appears to be connected with the body, both anteriorly and posteriorly, by semi- 
transparent membranes only. 
Specimens 4-0 millimeters long. — At this age (size) the notochord is bent upward 
prominently and the caudal fin is well formed, the rays now being in a horizontal 
plane. The upward curve in the notochord gives the tail the appearance of being 
heterocercal. A thickening of tis- 
sues has occurred in the area to be 
occupied by the base of the anal. 
A similar development is evident 
for the base of the soft dorsal. The 
hind-gut remains prominent and 
Figure 51 —Micropogon undulatus. From a specimen 2.5 millimeters the Vent is becoming situated near 
lon " the anal, the distance between it 
and the origin of the anal being shorter than the diameter of the eye. The pigmen- 
tation remains the same as in the very young, except for a few black chromatophores 
that now have appeared around the hind-gut. (Fig. 52.) 
Specimens 6.0 millimeters long. — At this size the soft dorsal and the anal fins are 
fairly well developed and it is possible to make a reasonably accurate count of the 
anal spines and rays. Some of 
the rays in the dorsal fin (espe- 
cially the posterior ones), however, 
are not fully enough formed to per- 
mit of enumeration. The caudal 
fin is well developed. The het- 
erocercal character of the tail is 
Still evident, but in addition to Figure 52 .—Micropogon undulatus. From a specimen 4 millimeters long 
the upward-curved notochord (now 
ending at the base of the upper raj^s of the fin), the backbone also has become visible 
at the base of the caudal. Pectoral fins for the first time are evident, but the ven- 
trals appear to be undeveloped. The mouth is still quite oblique but much less so 
than in the very young. (Fig. 53 is based on a specimen 7 millimeters long and, 
therefore, in general a little further developed than the specimen just described.) 
Specimens 10.0 millimeters long. — The soft dorsal is now fully formed; the 
spinous dorsal is only partly 
developed, as all the spines are 
not yet visible. The caudal fin 
is quite long and its posterior 
margin is strongly convex. The 
heterocercal character of the tail 
remains only faintly visible. The 
pectoral fins are fairly well 
Figure 53 . — Micropogon undulatus. From a specimen 7 millimeters long 
developed and the ventrals are 
just becoming visible appearing as slight tufts of membrane. (Fig. 54 is based on 
a specimen 12.5 millimeters long and, therefore, represents a stage in the develop- 
ment about midway between the 10-millimeter specimen just described and the 15- 
millimeter one described in the next paragraph.) 
Specimens 15.0 millimeters long. — No outstanding changes in development have 
taken place since a length of 10.0 millimeters was reached. The spinous dorsal is 
now well enough formed to permit of a reasonably accurate enumeration of the 
