OF THE CLASS INFUSORIA. 533 



climates ; but it is only in the seas of hot climates, or nearly 

 so, that we find an abundance of the coral polyp with a rocky 

 covering or coral case. 



Sometimes these aggregated polyps deposit in the interior 

 of the common tissue by which they are united, a horny or 

 calcareous matter, constituting a sort of interior stalk, which 

 branches out like a tree, in proportion as the animated mass 

 sends forth new branches. It is in this way that the coral 

 of commerce is formed (Fig. 189), of which such use is made 

 in the fabrication of ornaments : there is an active fishery for 

 this substance on the coast of Algeria. 



The actiniae belong to this division of the animal kingdom ; 

 they are also called sea anemones (Fig. 168) ; they have a 

 fleshy body, and are found in great numbers on the rocks of 

 our coast; the caryophylli and the astreae, which, more than 

 all others, assist in the formation of coral reefs (Fig. 190) ; 

 the coral animal itself (Fig. 189) ; the veretilli (Fig. 559), 

 which do not adhere to the soil, but are simply buried in 

 the sand by one of the extremities of the common stalk, 

 belong to this division. Most zoologists also class with 

 them the hydra, of which we have already spoken ( 347). 



OF THE CLASS INFUSOEIA PROPERLY SO CALLED.* 



622. Those animalcules which can only be detected by 

 the microscope, or which, even to a late period, have been 

 confounded with the rotifera ( 586), but whose structure is 

 very different, are developed in abundance in water containing 

 the remains of organized bodies. Their body, sometimes 

 rounded, sometimes elongated, is often covered with small 

 cilia, and offers in its interior a number, generally very con- 

 siderable, of small cavities, which seem to perform the func- 

 tions of stomachs. In some, these little enlargements seem 

 to be grouped around a canal which opens externally by 

 two extremities (Fig. 192) ; but at other times they seem to 

 be altogether isolated ; and persons who have made these 

 little beings the object of a special study, are not agreed as to 

 the existence of a direct communication between this cavity 



* Many of the small beings which zoologists place in this group appear 

 rather to belong to the division mollusca than to that of ?oophytes; but 

 their natural affinities have not as yet been so clearly established as to enable 

 us to discuss this question here. 



