370 E. W. MACBRIDE. 
Fig. 89 is a section of a larva of Stage D; both hydrocceles 
are well developed—the right, in fact, better than the left; the 
Bre. HIG: 
right hydroccele appears on the left side of the figure, since by 
an oversight the section was drawn from the wrong aspect. It 
took me some time in this larva to determine which side was 
which, but the right hydroceele is rather more dorsally situated, 
and opens by only a narrow slit into the anterior celom. It is 
also curved somewhat differently, the most posterior lobe being 
No. 4, not No. 3, as on the left side. Fig. 90 shows a most 
remarkable variation. We see a pore opening directly from the 
hydroceele to the exterior. If, as I shall attempt to show later, 
the anterior coelom may be compared to the proboscis cavity of 
Balanoglossus, and the two hydroceeles to the collar cavities of 
that animal, we see that what we may terma collar-pore may 
arise as a variation. Figs. 91—94 are sections taken from a 
larva of Stage G. Its only abnormality is that in connection 
with the right hydroccele, which is of normal character, a 
second pore-canal and stone-canal are developed. Fig. 92 
should show the opening of the second stone-canal into the 
hydroceele, but the lithographer has unfortunately not brought 
out the slit-like opening ; fig. 93 the opening of conjoined pore- 
canal and stone-canal (compare woodcut 3) into the axial sinus. 
Fig. 91 shows that the two pore-canals unite, to open by a 
common median pore. The above are not by any means all 
the variations observed, but they are sufficiently typical to in- 
dicate their nature. 
