86 HENRY BURY. 
it is worth while to remember, though no great stress can be 
laid upon it, that the cavities of the arms, bothin Crinoids and 
Asterids, are primarily parts of the left body-cavity only, though 
in both these forms (but not apparently in Ophiurids) the 
right cavity secondarily extends into them. 
Erratum.—lI take this opportunity of pointing out that the 
calcareous plate marked over the “ anterior enterocel” in 
fig. 4 of my former paper (5) is entirely due to a lithographer’s 
error. A similar error has caused the omission of the madre- 
porite in Bipinnaria (8, fig. 14). 
E. CRINOIDS. 
The development of Antedon rosacea, which alone among 
Crinoids has been studied, is too well known to need any 
description here; and though Seeliger’s (80) careful examina- 
tion, while undoubtedly correcting some of my errors (4), con- 
tains much debatable matter, yet fortunately few of the 
points to which I wish here to call attention are open to 
dispute. 
(1) The plane of the hydrocel is not parallel to that of the 
mesentery in the larva, but forms an angle with it. I may 
have exaggerated this in my figure (4, fig. 59), but it is un- 
questionably very marked (80, pl. xvi, fig. 67), and may be 
compared with the somewhat similar, though by no means 
identical arrangement in Asterina (15, woodcut iii, p. 156). 
(2) The stalk, though connected with the preoral lobe of 
the larva, does not include in the adult the whole of this lobe; 
while it does contain in the larva other parts which do not 
seem primarily to belong to this region. Thus the anterior 
body-cavity, which extends into this region in all larve which 
possess a preeoral lobe, is far removed from the stalk in the 
Cystid stage of Antedon ; while several skeletal plates, and part 
of the right body-cavity, are present in this region of the 
larva. Now whatever may be said about the identification 
of the terminal plate of the stalk with the dorso-central of other 
Echinoderms, we have strong reasons for thinking that the 
ancestral Crinoid (like many Cystidea) was sessile; and there- 
