128 HENRY BURY. 
ported by evidence. Spengel’s idea evidently is that the whole 
hydroceel ring is comparable to the two collar-cavities combined ; 
and if there were any evidence of its two-fold origin, we might 
readily adopt this view. It is just conceivable that the varia- 
tion in the point of closure of the ring is in some way connected 
with this, and that the hydrocel really does contain in itself a 
right and a left element—its present development on the left 
side alone being almost exactly paralleled by the development 
of the right body-cavity in Auricularia from the asymmetrical 
(left) hydro-enteroccel rudiment. But on this point I refrain 
from offering an opinion. 
As to MacBride’s “ collar-pore ” in Asterina, I would point 
out the a priori improbability that the ancestral Echinoderm 
ever possessed such a pore ; for if it did, why has the hydrocel 
lost it own pore, and entered into a secondary connection with 
that of the anterior enteroccel? Until further examples of its 
occurrence have demonstrated a constant position for this pore, 
it seems to me far more probable that we have in it simply 
a case of multiplication of water-pores, such as has led in 
Rhizocrinus to the presence of one in each interradius. 
To the resemblances above mentioned, and some urged by 
Morgan (22 and 23), I would suggest the addition of others, 
which, if supported by further investigations, would go far to 
bind the two groups together. The suggestions are not wholly 
new, various scattered hints at them being found in the pages 
of other writers; but the present paper offers, I think, far more 
evidence than has hitherto been attempted. 
At the base of the proboscis of Balanoglossus lies a*closed 
vesicle ( pericardium,” ‘‘ Herzblase,’ “sac of proboscis 
gland”), which is dorsal to the alimentary canal (notochord), 
and, being in the middle line, has the water-pore on its left. 
Underneath this “ pericardium,” and deriving its muscular coat 
from it, lies the pulsating organ known as the “heart” it is 
simply a lacunar space, as are the blood-vessels with which it 
communicates, and may be regarded as a remnant of the em- 
bryonic segmentation-cavity. 
In intimate connection with these structures is the “ pro- 
