18 
MONICA TAYLOR. 
being flat. It will be remembered that in Stage 30 branchial 
respiration was just beginning, and that the pectoral fins 
ceased growing as soon as branchial respiration was well 
established. In Stage 34 the fins shrivel and fall off bodily, 
the discarded fins measuring about 1’5 mm. in length. The 
stumps^’ are, however, recognisable in the sections for some 
time longer. Quantities of these discarded fins are to be 
found lying on the bottom of the tanks containing living 
larvas of this and the succeeding stages. The fins in Stage 
30 are situated just posterior to the opercular opening. In 
Stage 32, however, the hind end of the operculum has reached 
the point of origin of the fins, as may be seen in PI. 3, fig. 19. 
In Stage 33 operculum and branchial cavity have become 
elongated to such an extent that the fin stalks are ac- 
tually covered by the operculum, and can only gain exit from 
the branchial chamber on the ventral side (PI. 2, figs. 14 
and 15), the gill-chamber opening by this time having nearly 
assumed its adult position and size. 
The pressure of the edge of the operculum on the base of 
the fin is possibly responsible for the degeneration of the 
tissues in the stalk — thus enabling the main part of the 
fin to drop off. On the other hand, it is quite possible that 
the shedding of the fins is a natural selection phenomenon, 
the fins tending to degenerate at their base at the period 
when they become covered by the operculum without there 
being any direct mechanical effect. The next stage (34, 
which is not figured) is marked by absence of fins, a more 
anterior position of the eyes, and by the extension of the liver 
to the level of the anus. 
In Stage 35 (PI. 2, fig, 16) the larva has practically 
assumed its adult form, though head and branchial regions 
are perhaps more distinctly distinguishable from the rest of 
the body than they are in the full grown specimen. There is 
no sign of pectoral fins and no trace of rostrum. The crea- 
ture is eel-like in shape, the body behind the opercular 
cavity being almost perfectly cylindrical, while the hinder 
part of the trunk, becoming gradually more laterally com- 
