44 
ZOOLOGY. 
Fig. 44. — Bipinnaria with the star- 
fish budding: from it. e, e\ d' , g, 
g\ protuberances of the body 
comparable with the "arms" of 
the Brachiolaria figured in the 
adjoining engraving. 5, mouth; 
o, vent of the larva; A. germ of 
the star-fish; h, ciliated digestive 
tract; i, ambulacral rosette (germ 
of the water-vessels). 
Fig. 45.— Brachiolaria of As- 
terias vulgaris, enlarged, 
with the star-fish (r) devel- 
oping at the aboral end. 
e, median anal arm ;e^, odd 
terminal oral arm;/, brach- 
iolar arm ; /, branch of wa- 
ter-tube {v w') leading into 
f odd brachiolar arm; f", 
surface warts at base of odd 
brachiolar arm 
Class III. — Echi^^oidea {Sea-iircliins). 
General Characters of Sea-TJrchins. — A good idea of the 
general structure of sea-urchins may be obtained by an ex- 
amination of the common sea-urchin, EcTiinus (Fig. 46), 
Fig. 46.— The common Sea-urchin, Echinus drobachiensis. d, framework of 
mouth and teeth seen in front; c. the same seen sideways; a, b, side and ex- 
temal view of a single tooth (pyramid); all natural size. 
