ZOOLOGY 
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Fia. 151.—View of the internal organs of a Holothurian which has been cut open 
ie 
to 
a ew) 
along the middle dorsal line. 
6. 
Radial ossicle of the calcareous ring, 
into which the longitudinal muscle 
is inserted. 
Interradial ossicle of the calcareous 
ring. 
Radial water-vascular vessels. 
Circumoral ambulacral ring. 
Polian vesicle. 
ice) Coy 
From Leuckart. 
Two stone canals ending in Madre- 
poric plates; the upper one is 
attacaed to the dorsal mesentery, 
the lower one hangs freely. 
Circumoral blood-vessel. 
Ventral blood-vessel. 
Dorsal blood-vessel. 
Anastomosing branch between dif- 
ferent parts of the ventral blood- 
vessel. 
