THE DEVELOPMENT OF SYMBRANCHUS MARMOJJATUS. II 
and dorsal to the braiicliial regions. An operculum barely 
covering the first branchial arch is visible in horizontal 
sections. The pectoral fiig the anterior edge of which curves 
backwards, now measui-es about IT mm. in length. The liver 
is visible on the left side in the xylol specimens. 
Dr. Agar describes in his notes a pigment-spot on the left 
side of the creature as being conspicuous in the fresh speci- 
mens. In the early stages, i.e. forty hours after hatching, 
this pigment-spot lies anterior to the middle point of the 
attachment of the yolk sac. Its position is relatively further 
back in the later stages of development and more superficial. 
No trace of this pigment-spot can be found in the pi-eserved 
specimens, but in those stained and cleared in xylol the gall- 
bladder is distinctly visible in the position described in the 
notes, and a consultation of the sections leaves little doubt 
that the gall-bladder is responsible for the spot. 
Stage 26 (PI. 1, fig. 9). — The coiled portion of the body 
alluded to above straightens out as the creature grows, so that 
at this stage (26) a straight line joining the tip of the rostrum 
to the tip of the tail measures 7 mm. The rostrum has 
lengthened and lies parallel with the curve of the yolk-sac. 
The pectoral fins are about 1°5 mm. in length. The cerebellum 
rudiment is conspicuous (c. r., PI. 1, fig. 9) ; the eye is more 
lateral in position. The operculum covers the first two 
branchial arches. 
Stage 27. — Seventy hours after hatching the creature is 
about 9 mm. long, the true tail being' about 2'o mm. Its 
general appearance has, howevei', undergone little change 
from the conditions shown in PI. 1, fig. 9. The pericardial 
space has increased in depth. The head is becoming more 
opaque. 
In Stage 28, the rostrum, on account of the growth of 
the brain, nose and eyes would now be described more cor- 
rectly as a dorsal cephalic process than as an anterior one. 
The subintestiual vein (PI. 1, fig. 9) is conspicuous in the 
figures of this and succeeding stages, and a sketch of the 
living creature among Dr. Agar’s field notes shows that it is 
