Fig. 
Fig. 
dQ JQ dQ dO 
wy? 
ig. 20. 
ie 2, 
22. 
23. 
24. 
ECHINUS. 323 
A rotula. Nat. size. 
An alveolus, viewed from lateral faces. Nat. size. 
An alveolus, viewed from outer surface. Nat. size. 
A transverse section of an alveolus, to show the 
position of the tooth. Nat. size. 
‘* Aristotle’s lantern,’ after removal of two of 
the alveoli to show the pharynx. Nat. size. 
PATE) 
A tridactyle pedicellaria. Xx 20. 
A gemmiform or glandular pedicellaria. x 20. 
An ophiocephalous pedicellaria. xX 20. 
Longitudinal section of the decalcified head of a 
small tridactyle pedicellaria. xX 175. 
One of the blades of the head of a trifoliate 
pedicellaria.  X 180. 
. 18. Verticai section of decalcified spheridium. x 175. 
tee 19; 
Head ot a small ophiocephalous pedicellaria 
from the peristome. x 60. 
A small portion of the periphery of a decalcified 
spine. xX 350. 
Longitudinal section of the decalcified head of 
a glandular pedicellaria. » 175. 
Transverse section of the decalcified head of a 
glandular pedicellaria. x 80. 
Puate III. 
Dissection to show the muscles and lizaments 
of the masticatory apparatus, and the principal 
canals of the water-vascular system. X 2. 
Part of a sagittal section of the apical system, 
showing the pores of the madreporite, madre- 
poric ampulla, water-tube, axial sinus, and 
central plexus. Slightly diagrammatic. x 20. 
