LARVAL TELEOSTS 223 
shark larva of Fig. 286: dorsal, caudal, and anal regions are 
outlined in the unpaired fin; a pectoral fin of a fin-fold 
character, P/, has appeared; the spiracle, SP, is becom- 
ing established. The mouth region is more clearly indi- 
cated in this stage, S, but may better be seen in ventral 
view in a slightly later larva; here (Fig. 299) the posterior 
lip is constricted off from the yolk region, and the anterior 
lip is budding off near the median line a pair of the tactile 
barbels ; the dermal fold (operculum) enclosing the gills 
is in a condition very similar to that of Ceratodus in 
Fig. 293. A larva of the fourth day (Fig. 300) shows 
well-marked advances : the snout is elongated ; the opercle 
is enclosing the gills, which are now seen to protrude as 
external branchial; the pectoral fin elongates and is tend- 
ing to protrude its fin axis; body segments and heart are 
encroaching into the region of the now elongate yolk sac; 
the lateral line has been formed. In a larva of four weeks 
(Fig. 301), the essential outlines of the sturgeon may be 
recognized, although the head appears of strikingly larger 
proportions: barbels, nares, mouth, operculum, and spiracle 
are as in the adult ; fins, of the mature outlines, are want- 
ing in all save basal supports ; yolk material has long since 
been exhausted. A very late larva (Fig. 302), supposed to 
be twelve months old, differs outwardly from the sexually 
mature form in but its colouring and dermal plates: those 
of the regular rows are of great size, conspicuous in their 
abrupt spines and well-roughened borders ; and those of the 
remaining trunk integument are remarkably prominent ; the 
tail of the larva shows clearly its palzoniscoid character. 
V. Larval Teleosts 
The metamorphoses of the newly hatched Teleost 
must finally be reviewed; they are certainly the most_ 
