i;8 THE SCIENCE OF LIFE. 



are supplied with distinct sets of muscles. Cilia are 

 present on the digestive tube, producing a current both 

 respiratory and circulatory. 



The Actinia, or Sea-anemones, are the much-admired 

 forms so often seen in the rock-pools around our shores, 

 sometimes called animal flowers, attached to the rocks 

 by a flat disk, expanding their petal-like tentacles in 

 search of prey, and, when uncovered by the retreating 

 tide, contracting into small round gelatinous masses. 



A B 



FIG. 78. A. Sea-anemone, seen from above. B. Section of Sea-anemone, a. Cavity 

 of stomach, b. Surrounding chambers. 



The tentacles and partitions of the body are in multi- 

 ples of six. Fig. 78 represents the internal form of 

 Actinia. 



The Coral polyps are Actinozoa, which secrete coral, 

 generally composed of carbonate of lime, but it is occa- 

 sionally horny, or a mixture of horny and calcareous 

 matter. These polyps are usually found in colonies 

 formed by a continuous process of budding. The com- 

 pound mass is like a sheet of animal matter, fed and 

 nourished by numerous mouths and many stomachs. 

 Corals are of two kinds, the sclerobasic and sclerodermic 

 corals. The polyps of the latter resemble Actiniae in 

 structure. The earthy matter is secreted between each 



