THE MET AZOA DIVISION OF LABOR 



209 



A branching maclreporic coral. 



because, when expanded, it looks like a beautiful flower of a golden yellow 

 or red color. The body of the sea anemone is like the hydra, a column 

 attached at one end. The free end is provided with a mouth surrounded 

 with a great number of tentacles. These, when expanded, look like the 

 petals of a flower. The sea 

 anemone is a very voracious 

 flower, for by means of the bat- 

 teries of stinging cells in its ten- 

 tacles it is able to catch and 

 devour fishes and other animals 

 almost as large as itself. When 

 disturbed or irritated, the ani- 

 mal contracts into a slimy ball, 

 making it difficult to dislodge 

 from its attachment. 



Although the sea anemone is 

 like a large hydra in appearance. 

 its interior is different. The 

 hollow digestive cavity contains 

 a number of partitions more or 

 less complete, which run from 



the outer wall toward the middle of the cavity. These partitions, known 

 as mesenteries, are found in pairs. Part of the cavity, as in the hydra, 

 is given up to digesting the food. Food is killed by means of stinging 

 cells found in the long threadlike tentacles. 



Coral. If a piece of madreporic coral is examined with a hand lens, a 

 number of little depressions will be seen in the 

 limy surface, each of which has tiny partitions 

 within it. 



These cuplike depressions were once occu- 

 pied by the coral animals or polyps, each in its 

 own cup. The mesenteries of the coral polyp 

 are paired and hollow on the under surface. 

 The partitions seen in the coral cups lie be- 

 tween the pairs of mesenteries, and are formed 

 by them when the animal is alive. Sea water 

 has a considerable amount of lime in its 

 composition. This lime (calcium carbonate) is 

 taken from the water by certain of the cells of 

 the coral polyp and deposited around the base 

 of the animal and between the mesenteries, 

 thus giving the appearance just seen in the 

 cups of the coral branch. 



Asexual Reproduction. These polyps reproduce by budding, and 

 when alive cover the whole coral branch with a continuous living mass of 



HUNT. ES. BIO. 14 



A single coral cup, showing 

 the walls of lime built by 

 the mesenteries. From 

 a photograph loaned by 

 the American Museum 

 of Natural History. 



