108 INVERTEBRATE MORPHOLOGY. 



becomes moulded over it (Fig, 59), so that it forms a central 

 horny or more or less calcified axial support, and in addition 

 the mesogloeal cells secrete scattered 

 particles of carbonate of lime, having a 

 more or less definite form for each spe- 

 cies, but not uniting together to form a 

 firm skeleton. 



The development of the Anthozoa is 

 always direct, and the diploblastic 

 Pig. 59. — Diagram of condition is produced by delamina- 

 YouNQ GoBGONiAN (af- tion of the cells of the blastula. Many 

 ervoN ocH). adult forms possess the power of 



division, either transverse or longitudinal, the latter giving 

 rise to complex colonies in many cases. In other forms the 

 primary polyp may develop a stolon from which other indi- 

 viduals may bud, producing a diiiuse colony, or the intervals 

 between the individuals may be filled up by a growth of 

 mesoglcea traversed by a network of canals, forming a tissue, 

 the coenenchyme (Fig. 60), in which the various individuals are 

 imbedded. 



The class Anthozoa may be divided into a number of 

 orders, whose existence depends mainly on the arrangement 

 of the mesenteries. 



1. Order Alcyonariae. 



The majority of the Alcyonarians produce colonies by bud- 

 ding. In some the individuals are scattered on stolons, in 

 others imbedded in a coenenchyme {Alcyonium, Fig. 60), or in 

 others united to form fleshy colonies of a feather or reniform 

 shape {Renilla), the whole being imbedded in the sand by a 

 fleshy stalk. In some of the groups a horny or calcareous 

 skeleton is present in addition to the calcareous spicules im- 

 bedded in the mesoglcea and may form a central axis enclosed 

 by the coenenchyme (Fig. 59) and of a horny consistency, as in 

 Gorgonia and Leptogorgia, or more or less calcareous, as in 

 Isis and Corallium, the skeleton of the latter constituting the 

 red coral of commerce. In the Organ-pipe Coral, Tvhipora, 

 each individual lives in a calcareous tube, the various tubes 



