CORALS AND CORAL ARCHITECTURE. 



261 



the sea-water passes freely, and carries the digested food through the 

 internal cavities. There is no other circulation of fluids/ 



Fleshy folds or partitions extend from the upper to the lower end 

 of the animal, and give to the polype the appearance of a little balloon 

 of tissue-paper crumpled up. These radial folds in the animal's struct- 

 ure are illustrated in Fig. 3, page 260, which is an ideal sectional 

 view of one of this class of animals. The radiating partitions or folds 

 are seen to be arranged in pairs. In the coral-secreting polypes these 

 pairs are six or five, or multiples of six or five. The space between 

 each of these partitions opens into the tubular tentacle at the top of 

 the animal. The tentacles of the polypes moving freely and with con- 



Fig. G. 



Coral from the Feejees, called Astrccce, from the Star-shaped Cells. 



siderable muscular strength, seem sufficient to supply the animal's 

 wants, but it has a formidable armature in the stinging barbs which 

 cover its tentacles, mouth, and stomach, and which produce torpor and 

 death in any small animal brought in contact with them. These are 

 called lasso-cells. The cells in which the lasso or barbs are located 

 measure from -g-tg of an iuch to %-J^ of an inch in length. From 

 these the lasso is projected, inflicting, in some species, upon even a 

 human hand, painful and serious injury. Owing to this peculiarity of 

 certain jelly-fishes, they have been appropriately named sea-nettles. 



Between the fleshy partitions of the polype's body are thin, stony 

 plates. These, with the other hard portions, make up the coral skele- 

 ton, and are wholly secreted by the polype. Fig. 4, page 260, repre- 

 sents a group of polypes (Phyllangia Americana) from the West In- 

 dies, and illustrates well the radial structure of the cells. 



The secretions occur around and underneath the polype, never in its 

 interior, which would interfere with its functions. It constructs its 

 skeleton by secretion, as an oyster does its shell, or as the tissues of a 



