CCELENTERATA : ACTLNOZOA. 107 



The Alcyonaria differ mimerically from the Zoantharia in 

 having their soft parts arranged in multiples of four, instead 

 of five or six, as in the latter. Their tentacles, too, are pin- 

 nate, and are not simply rounded. Numerically the Alcyonaria 

 agree with the extinct order Rugosa, but the latter invariably 

 possess a well developed sclerodermic corallum, the thecae of 

 which exhibit either septa or tabulae, or both combined. 



With the exception of the single genus Haimeia, the 

 Alcyonaria are all composite, their polypes being connected 

 together by a common ccenosarc, 'through which permeate 

 prolongations of the somatic cavity of each, forming a sort of 

 canal-system, whose several parts freely communicate,' and 

 permit of a free circulation of nutrient fluids. Anatomically 

 the polypes of the Alcyonaria do not differ in any essential 

 particular from those of the Zoantharia ; the numerical dis- 

 tinction being the one by which they are chiefly separated 

 from one another. The Alcyonaria are divided into four families, 

 viz. the AlcyonidoB, the Tubiporidce, the Pennatulidce, and the 

 Gorgonidce. 



FAMILY I. ALCYONID^. This family is characterised by the 

 possession of a fixed actinosoma, which is provided with a 

 sclerodermic corallum in the form of calcareous spicula im- 

 bedded in the tissues. 



Alcyonium may be taken as the type of the family, and it is 

 well known to fishermen under the name of 'Dead-men's 

 fingers.' It forms spongy-looking, orange- coloured crusts or 

 lobate masses, which are attached to submarine objects, and 

 are covered with little stellate apertures, through which the 

 delicate polypes can be protruded and retracted at will. The 

 polypes communicate with one another by an anastomosing 

 system of aquiferous tubes, and the corallum is in the form of 

 cruciform, calcareous spicula scattered through its substance. 



FAMILY II. TUBIPORID.E. In the Tubiporidce, or ' organ-pipe 

 corals,' of which T. musica is a familiar example, there is a 

 well developed sclerodermic corallum, with thecae, but without 

 septa. The corallum is composed of a number of bright red, 

 tubular, cylindrical thecae, which are united together externally 

 by horizontal plates or floors, which are termed ' epithecae,' 

 and represent external tabulae. The polypes are usually bright 

 green in colour, and possess eight tentacles each. 



FAMILY III. PENNATULIDJI. The Pennatulidce, or ' Sea-pens,' 

 are defined by their free habit, and by the possession of a 

 sclerobasic, rod-like corallum, sometimes associated with 

 sclerodermic spicules. 



Pennatula, or the ' Cock's-comb,' consists of a free coenosarc, 

 the upper end of which is fringed on both sides with feather- 



