Ill] 



ZOANTHARIA 



73 



siphonoglyph (Gr. on'^coi/, a tube; yA.w, to hollow out) and its 

 cilia keep up an inward current of water whilst the rest of the 

 gullet is choked with prey, and so fresh supplies of water charged 

 with oxygen are brought in contact with the lining of the coelenteron 

 and enable it to respire. The two mesenteries with which the lower 

 end is connected are called the directive mesenteries, they are 

 situated opposite to the two ciliated mesenteric filaments. By the 

 cooperation of the latter with the siphonoglyph complete circulation 

 of the water in the coelenteron is maintained. The ectoderm of 



11 





FIG. 32. Semi-diagrammatic view of half a simple Coral, partly after G. C. 

 Bourne. On the right side the tissues are represented as transparent to 

 show the arrangement of the theca and septa ; on the left side a mesentery 

 is seen. 



1. Tentacle. 2. Mouth. 3. Oesophagus. 4. Mesentery. 5. Mesen- 

 teric filaments, free edge of mesentery. 6. Ectoderm. 7. Endoderm. 

 8. Basal plate. 9. Theca. 10. Columella. 11. Septum. 



course gets its oxygen directly from the surrounding water. When 

 the polyp of an Alcyonium colony seizes its prey it presses its victim 

 through the stomodaeum into the coelenteron where it is gripped by 

 the inner edges of the eight mesenteries. The stomodaeum and the 

 six glandular inesenterial filaments secrete a juice to be compared 

 to the human saliva which disintegrates the flesh of the victim and 

 causes it to break up into small fragments, these are then swallowed 

 by the endoderm cells covering the mesenteries, especially by those 

 lying immediately behind the filaments. 



The ordinary sea-anemones or Zoantharia differ from Alcyo- 



