2 HENRY BURY. 
of the larva of Asterina is not only the subject of Ludwig’s 
well-known paper, but has recently received further attention 
from MacBride(19), whose full account may be expected shortly. 
- It is unnecessary, therefore, for me to spend time on a detailed 
description, and I may confine my account entirely to those 
points which bear most on my theoretical views, and those 
which the absence of the intestine in the larval Asterina tends 
to obscure in that form. 
As already mentioned, most of my material was obtained at 
St. Andrews; but the earlier stages have been more especially 
studied in larva, probably of Asterias glacialis, obtained at 
Naples. 
There is no need to describe here the earliest stages of all, 
as the few points in which my observations are at variance 
with Field’s (8) have no special connection with the present 
paper. 
The hydroccel seems to be always marked out before the 
left posterior body-cavity is separated off, but the exact form 
of the ccelom at this stage is subject to much variation; 
fig. 17, however, may be taken as a fairly typical example. 
In the next stage, in all cases examined by me, the separation 
of the posterior enteroccl from the combined anterior en- 
teroccel and hydroceel is complete. The posterior cavity then 
pushesa “dorsal horn” forwards on the dorsal side, close upto the 
water-pore, while a “ ventral horn” growsrapidly forwards along- 
side the intestine, and then, at the point at which the latter 
(closely pressed against the intestine throughout most of its 
course) curves outwards towards the anus, this “ ventral horn” 
of the left body-cavity crosses over to the right side. Meeting 
with no opposition from the right body-cavity, which at this 
stage only reaches the ventral surface at its posterior end, the 
“ventral horn” widens out, and passes down the right side of 
the intestine, near the posterior end of which it meets the 
right body-cavity, and forms with it an oblique mesentery, 
shown in fig. 27. All the stages of this movement can, in 
perfectly healthy larvee, be easily followed in the living animal, 
from which fig. 27 is drawn; but I have fully confirmed the 
