METAZOA COELENTERA. 125 



than the Hexactiniae, since the latter are bilateral in early 

 life and become radiate afterward, owing to attachment 

 and the action of physical forces. 



Another colonial form is Veretillum (No. 180) which 

 is related to Renilla. 



Briareum (No. 181, see upper shelf) of the Gorgon- 

 acea is an upright, irregularly lobed colony. The 

 zoons are without protecting cups and can be entirely 

 withdrawn into the coenenchyma which is abundantly 

 supplied with spicules. The central mass, which can 

 hardly be called an axis, is supplied with nutritive canals. 



In Melitodes, (No. 182, M. ochracea Verr.), the axis is 

 jointed and the sections consist of alternating portions of 

 horny and calcareous matter. The horny sections are in 

 reality made of a horny substance and loose spicules, 

 while the calcareous parts are composed of consolidated 

 spicules. All the joints are penetrated by canals. 



The spicules in Corallium rubrum Linn. (No. 183), 

 unite to form a dense calcareous axis (No. 184), which 

 is a beautiful red color and used for ornaments. The 

 young coral animal ha's a mouth surrounded by eight 

 white, pinnate tentacles (No. 183). The internal bag 

 leads into the body cavity which is divided by eight 

 mesenteries into eight chambers. The outer flesh is a 

 bright red color and is stiffened by spicules. This single 

 zoon buds and a colony arises. The body cavities of all 

 the zoons connect with a series of water tubes ; these 

 press upon the calcareous stem which is secreted by the 

 bases of the zoons and while it is yet soft, indent its 

 surface. 



Isis (No. 185) has a jointed axis consisting of horny 

 and silicious sections. The zoons can be withdrawn into 

 the thick coenenchyma. The spicules are club-shaped 

 and stellate in form. 



An upright colony is formed by Xiphigorgia (No. 186). 

 A related form, Plexaura (No. 187), has a horny axis, 

 while the coenenchyma has variously shaped spicules. 



