248 



ZOOLOGY 



Fio. 151. — View of the internal organs of a Holothuriau which has been cut open 

 along the middle dorsal line. From Leuckart. 



1. Badial ossicle of the calcareous ring, 



into which the longitudinal muscle 

 is inserted. 



2. Interradial ossicle of the calcareous 



ring. 



3. Badial water-vascular vessels. 



4. Circumoral ambulacra! ring, 



5. Polian vesicle. 



6. Two stone canals ending in Madre- 



poric plates ; the upper one is 

 attacaed to the dorsal mesentery, 

 the lower one hangs freely. 



7. Circumoral blood-vessel. 



8. Ventral blood-vessel. 



9. Dorsal blood-vessel. 



10. Anastomosing branch between dif- 

 ferent parts of the ventral blood- 

 vessel. 



