ACTIXOZOA. 85 



The Actinozoa are divided into four ordei-s — viz., the Zonntliaria, 

 the Alcyonaria, the Rugosa, and the Ctenophora. 



Order I. Zoantiiaria. 



The Zoantiiaria comprise those Aetinozoa in which the polypes 

 are furnished with smooth, simple, mually numerous tentacles, which, 

 like the mesenteries, are in multiples of six. The Zoantiiaria are 

 divided into three groups, distinguished from one another by the 

 presence or absence of a coral, and by its structure when present. 



The first of these groups is termed Zoantharia malacodermata, or 

 "soft-skinned" Zoantharia, because the polypes are either wholly 

 destitute of a qoral, or if there is one, it consists merely of little 



Fig. 48. — Actinia mesemhryantliemum, one of the Sea-Anemones. 

 (After Johnston.) 



scattered spicules of carbonate of lime or grains of sand. Generally, 

 too, the organism is simple, and consists of no more than a single 

 polype. The best known of the members of this group are the 

 beautiful Sea-anemones or " animal-flowers " (Actinidce), which occur 

 so plentifully on every coast (fig. 48). It will be as well to describe 

 the structure of a sea-anemone somewhat in detail, as in this way 

 a clear notion may be obtained of the general anatomy of the 

 Actinozoa. The body of an ordinary sea-anemone (fig. 48) is a 

 ti-uncated cone or short cylinder, termed the " column," and is of a 

 soft leathery consistence. The two ends of the column are teiTaed 

 respectively the "base" and the "disc," the former constituting a 

 kind of sucker, by means of which the animal can attach itself at 



