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ME. G. J. ROMANES AND PROFESSOR J. C. EWART 
r 
Fig. 11. 
o 
Fig. 12. 
Fig. 13. 
Fig. 14. 
Fig. 15. 
/. “ Tree-like organ.” 
m. Membranous wall of large space above “tree-like organ.” 
n. Sinus around tip of tooth 
o. Tooth lying in space (p) between the alveoli. 
q. Edge of alveolus. 
r. Interalveolar muscle. 
. 9 . Auricle. 
t. Radial nerve. 
Ambulacra! system— Solaster. 
a. Madreporic canal. 
b. Inner end (g) outer end of sinus leading to circular neural vessel ( h) 
from which radial neural vessels (/) arise. 
c. d. Polian vesicles. 
f. Ampullae. 
m. Oral aperture. 
n. Madreporic plate. 
Madreporic plate enlarged, showing space (a) through which fluid escapes 
from madreporic canal. 
Scheme showing portions of ambulacral and nervous systems of Echinus, 
a. Ampullae. 
h. Radial nerve. 
c. Neural radial sinus. 
cl. Lining membrane of shell. 
e. Radial ambulacral canal. 
/. Lateral branch of radial canal. 
g. Pedicel. 
h. Spine. 
i. Pedicellaria. 
k. Layer of fibres external to shell. 
l. Subepidermic nerve-plexus. 
/'. Plexus extending over base of spine. 
I". Plexus extending over pedicellaria towards base of mandibles. 
m. Epidermis. 
n. Lateral branch from nerve-trunk. 
o. Continuation of lateral branch alongside of pedicel. 
p. Portion of lateral branch which probably communicates with external 
plexus. 
r. Ambulacral plate. 
Fibres and cells of nerve-trunk. 
External plexus partially covered by epidermis lying over muscular and 
connective tissue-fibres. 
