COKALLINES. 



131 



are of two kinds (Fig. 52); the one, comparatively very large, is 

 imbedded in the axis, and disposed in parallel layers ; the others are 

 regular and much smaller. They form a network of unequal meshes, 

 which occupies the whole thickness of the external crust. This net- 

 work has direct and important connection with the polyps on the one 

 hand, and with the central substance which forms the axis on the 

 other. It communicates directly with the general cavity of the body 



Fig. 52. Circulating Apparatus for the nutritive fluids in the Coral. (Lacazo-Duthiers.) 



of the animal, by every channel which approaches it, while the two 

 ranges of network approach each other by a great number of anas- 

 tomosing processes. Such is the vascular arrangement of the coral. 



The circulation of alimentary fluids in the coral is accomplished by 

 means of vessels near to the axis, without, however, directly anasto- 

 mosing with the cavities containing the polyps which live in the 

 polypidom ; they only communicate with those cavities by very deli- 

 cate intermediary canals. The alimentary fluids they receive from the 



K 2 



