THE DEVELOPMENT OE SYMPHANOHHS MAKMOKATUS. 
9 
{I view of an egg* slightly older than the one just referred to. 
Idle main mass of the pectoral fins is about *3 mm. from the 
embryo proper, so that the fins look like two white mammilla) 
apparently unconnected with it (see also PI. 1 , fig. G, a 
slightly older stage). 
' Stage 23. — When the embryo is a little over five days old 
there is a curious proboscis-like structure (see PL 1, fig. 7), 
projecting freely from the extreme end of the creature more 
or less on a line with the mesencephalon. This rostrum is 
transparent and bluntly pointed and filled apparently with a, 
clear fluid. The tail is curled, though still in contact with 
the yolk. The pectoral fins are about *5 mm. in breadth and 
extend upwards and backwards over the yolk. The carti- 
laginous skeleton of the fin has made its appearance and is 
visible externally. 
Stage 24 (PI. 1. fig. 8) is the stage at which the embryo 
probably hatches out. The body of the creature has become 
much more cut off from the yolk, the rostrum projecting 
forwards anteriorly, the hind end being quite free. d’he 
heart is visible in the clear space separating the head from 
the yolk mass. The visceral arches are moi*e conspicuous ; 
ey^es and nostrils are ventral m position. Two rounded 
optic lobes anteriorly^ and a w^ell-marked very wide rhomb- 
encephalon posteriorly seem to be covered with a trans- 
parent lymph space continued into the rostrum already 
alluded to. The unpaired fin is beginning to grow. 
Stage 25 (slightly more advanced than PI. 1, fig. 8). — 
The embryo has now considerably^ lengthened, the posterior 
part being coiled as a result of this growth. As in the last 
stage, the head does not project freely from the yolk-sac 
except the rostrum, which is now extremely conspicuous, being 
about *7 mm. long. In some of the specimens particles of 
mud and debris are attached to the rostrum at its tip, 
which suggested that this structure might perhaps function 
as a cement organ. A microscopic investigation of such 
specimens has, however, given little, if any, suppoit to such 
an interpretation of the function of this curious appendage. 
