436 
H. BURY. 
system, while the right pouch formed the whole of the adult 
body-cavity. Now, the terminal plates (“ brachial plates ” ol 
his description) are undoubtedly formed to the right of the 
water-vessel (hydroccel), and hence Agassiz was led to speak of 
them as formed round the right {f water-tube ” (enterocoel ) ; 
and although subsequent writers must long have been aware 
that the left enterocoel pouch enters largely into the forma- 
tion of the adult body-cavity, yet they have made no fresh 
investigation into the relations of the terminals. It is 
not a little curious that the dorsal mesentery, separating 
the right and left enterocoels, is actually represented in 
one of Agassiz’ figures (2, pi. v, fig. 6) to the right of the 
terminals. 
The next plate to appear is the madreporite. It arises close 
to, but nearer the median line than, the water-pore, which 
before long it embraces. In one form of Bipinnaria, which I 
more than once obtained, it lay in the same straight line with 
the terminals ; but usually it is more to the right, as shown in 
fig. 14. In the larva from which this figure was taken the 
terminals only were present, but I have added the madreporite 
from another larva, in which it was precociously developed. 
It really belongs to a somewhat later stage. 
Seeing that the terminals, both in Asterids and Ophiurids, 
belong to the left enterocoel, and not, as hitherto supposed, to 
the right, it obviously becomes important to reconsider the 
position of the madreporic plate in the two groups. This 
plate and the other orals of Ophiurids have always been 
assumed to belong to the left enterocoel, and it is, I think, 
practically certain that this view is correct, though the only 
fresh evidence I can offer of it is derived from the position of 
the madreporite in the bilateral larva, in which it lies over the 
left anterior enterocoel. The question now arises, is it not 
possible that the madreporite of Asterids may also belong to 
the left side, and not, as hitherto asserted, to the right ? If 
this were so, the position taken up by Ludwig on other 
inappropriate expression “stone-canal” (= Steinkanal = canal de sable). 
Agassiz applies it to the coelom, and its derivative the hydroccel. 
