126 HENRY BURY. 
similarity ; but it is difficult to regard Auricularia as a primi- 
tive larval form, and even if we could, the details of the like- 
ness are not sufficiently strong to prove a common origin. 
Spengel ignores this resemblance, and suggests that Mor- 
gan’s mention of Auricularia is a lapsus calami for Bipin- 
naria,! though he does not himself attach any phylogenetic 
importance to the resemblance of this larva to Tornaria. But 
though these larve resemble one another in having the ciliated 
band divided into two at the anterior pole, yet it is impossible 
to regard this as a primitive feature in Bipinnaria, seeing that 
no other Echinoderm larva normally possesses it; while the 
ease with which it may be independently acquired is attested 
by the fact that I observed precisely the same division of the 
band into two, in one instance, in Auricularia. 
Of far more importance is the presence in Echinoderms as 
well as in Enteropneusta of at least one anterior body-cavity, 
opening by a pore at its posterior end on the left side of the 
body. My identification of this cavity in Echinoderm larve 
(see 4 and 5) has met with a good deal of opposition, it being 
by many regarded as a mere appendage to the hydroccel; but 
the facts (1) that it always arises as early as, often earlier than, 
the posterior cavities—generally earlier than the hydrocel ; 
(2) that it is constant in position, arising and remaining 
anterior to the stomach, with the pore at its posterior end; 
(3) that it always has thin walls, while the hydroccel after the 
first moment of its appearance has thick walls, seem to me to 
go far towards refuting this view, and establishing the primi- 
tive nature of the cavity in question. The homology of it 
with the proboscis cavity of Balanoglossus may not be so well 
established, but at least has too much plausibility to be lightly 
set aside. 
The existence of a second anterior cavity in many Echino- 
derm larve is of less importance, since it seems to carry us 
back to a far earlier period than the separation from a common 
stock of Echinodermata and Enteropneusta. There is no clear 
1 Morgan (22) has certainly made several statements about Auricularia 
which are true, I believe, only of Bipinnaria, 
