74 HENRY BURY. 
of schizocceel origin, lying over the posterior end of the 
cesophagus. I have cut numerous sections to satisfy myself 
that it has no connection with the celom, from which, indeed, 
in the earlier stages it is somewhat widely separated. In later 
stages the right body-cavity pushes its way up close to it, but is 
at no time connected with it. Field (8, p. 118) found the 
same cavity in Asterias vulgaris, and gives figures of its 
schizoceel origin; he seems, however, unaware that I had 
already drawn attention to it (5, p. 31). MacBride (19) does 
not mention it in Asterina, but describes a cavity, derived 
from the anterior enterocel, in apparently very nearly the 
same situation; this he regards as the homologue of the right 
collar-cavity in Balanoglossus ; but until a similar cavity has 
been found in other Echinoderms—and especially in one which 
conforms more nearly to the usual plan of development—this 
conclusion appears to be somewhat rash. 
In very old Brachiolariz, just before metamorphosis, I have 
in a few cases observed a faint pulsation in this region—appa- 
rently in the floor of this cavity ; but the opacity and activity 
of the larva make it very hard to study, and it is moreover 
much slower and less regular than in Echinid Plutei. 
Immediately under the ‘‘ dorsal sac” in older Brachiolariz 
lies the termination of the “ dorsal organ,” as seen in fig. 19; 
but this, and the ultimate fate of the dorsal sac, have been 
already described in connection with Bipinnaria asterigera. 
Metamorphosis is ushered in, in the larva of Asterias 
rubens, by the fixation of the larva by the knobbed arms of 
the Brachiolaria, and the ciliated pit which they surround; 
and this fixation, at first voluntary, very soon becomes as com- 
plete as in Asterina (19, p. 433). Then the preoral lobe 
shrivels up, and all that remains of it is a small stalk lying in 
the interradius of the adult anus (interradius E). The larval 
intestine and anus soon disappear, but the latter, when last 
seen by me, still lay nearly in the interradius of the water-pore 
(judging the interradii by the arm-rudiments, not by the 
hydrocel pouches), or perhaps rather more nearly opposite 
radius V, 
