Class 2. Anthozoa. 113 



parent only in exceptional cases ; as a rule they remain connected 

 and thus colonies arise. These usually consist of a great number 

 of individuals, and frequently attain a very considerable size. An 

 alternation of generations occurs but rarely, since the same indivi- 

 dual can reproduce both sexually and asexually. 



The Anthozoon leaves the egg as a larva without tentacles, 

 swimming about by means of cilia. Later it attaches itself and 

 attains the adult form. Only a few {e.g., the Actinians) retain 

 a capacity for locomotion throughout life, and even then to a very 

 limited extent. 



The Anthozoa, all of which are marine, are predaceous animals. 

 By means of their tentacles they seize their prey, paralyse it, and pass 

 it through the stomodteum into the digestive cavity. When 

 undisturbed, they remain with their tentacles quietly extended; if 

 irritated, the tentacles and all the soft portions of the body are 

 instantly contracted. 



Order 1. AlcyOnaria {Odactbua). 



The members of this group possess only eight mesenteries, and 

 corresponding with these, eight branched pinnate tentacles. 

 In the mesogisea there is a number of almost microscopic calcareous 

 spicules. These are provided with knobs or sharp points, 

 are of various colours, and are less numerous in the upper than in the 

 lower region of the body, so that the former can be retracted into the 

 lower firmer portion. The spicules, which are for the most part not 

 very closely connected, arise in cells which have wandered in from 

 the ectoderm. 



Only a very few species are solitary; most of them form 

 colonies. Occasionally the individuals of a colony are united by 

 thin stolons containing canals which are in communication with the 

 gastric cavities. More often, the lower, harder portions of the polyps are 

 united by large connecting regions (coenenchyme), consisting chiefly 

 of mesogisea, which may be perforated by numerous canals. These 

 canals are lined with endoderm, and put the individuals of the 

 colony in communication with each other (for the connection 

 of individuals in the Organ-pipe Coral, see below). The external 

 form of the colony is very varied ; not infrequently it is 

 arborif orm ; and then there is usually an axial skeleton 

 in the stem and branches, formed in the Red Coral by the fusion of 

 innumerable calcareous spicules, and consequently situated in the 

 mesogisea. The axial skeleton of the Gorgonidse is quite different in 

 structure : the young colony secretes a horny mass on its pedal 

 surface: between it and the foreign body to which it is attached. 



