416 
H. BUEY. 
the whole of the praeoral lobe ; and the hydrocoel, which arises 
as a pouch on the left side at the junction of the left enteroccel 
with the cavity of the praeoral lobe, has at first a portion of the 
coelom intervening between it and the wall of the stomach — a 
condition which I have not observed in any other Echinoderm. 
Subsequently the hydrocoel comes to lie close to the stomach, 
having, as already mentioned, a ventral as well as a dorsal 
communication between the anterior and posterior divisions of 
the coelom (17, p. 147, pi. ii, fig. 37). 
In a previous paper (7, p. 38) I put forward the view that 
the single large anterior enterocoel of Asterina might be primi- 
tive ; but I ought to have remembered its formation in Bipin- 
naria and Brachiolaria by the fusion of two primarily distinct 
cavities. Now, the larva of Asterina is probably a modified 
Brachiolaria (17, p. 154), so that we shall be more correct in 
assuming that in this, as probably in many other points, 
Asterina exhibits a secondary and abbreviated form of develop- 
ment. 
Crinoids. — The earliest formation of the enterocoel pouches 
and hydrocoel in Antedon rosacea (the only Crinoid yet 
studied), exhibits some peculiarities with which we are not at 
present concerned (see 5 and 7) ; we will pass at once to the 
stage in which the following divisions of the coelom are pre- 
sent : (1) a single median anterior enterocoel (called “ caual de 
sable ” by Barrois). At the close of the free-swimming stage, 
this opens to the exterior at its posterior end by the water- 
pore, situated on the left side of the larva ; (2) right and 
(3) left posterior enterocoels, one on each side of the stomach; 
these do not long retain their lateral position ; and (4) the 
hydrocoel, on the left side, between the anterior and the left 
posterior enterocoels ; at first it opens into the anterior en- 
terocoel, but this communication is soon closed. Although 
this anterior enterocoel usually occupies a median position in 
the praeoral lobe, I have little doubt that it is the homologue 
of the left anterior enterocoel of other Echinoderms, and, 
indeed, in many cases it lies distinctly on the left side. 
Holothurians. — For the early stages of development of 
