CORALLINES. 145 



longitudinal lines or septa, 'stretching between the membrane and the 

 central stomach, which divide the intermediate space into an equal 

 number of compartments. These lines not only extend to the base of 

 the tentacula, but run across the anal disk, and terminate in a central 

 mouth. The tentacula are short, obtuse, ciliate on the margins, and 

 strengthened at their roots by numerous crystalline spiculae. The 

 polyp cells are oval, placed just under the skin, and are the termi- 

 nating points of certain long canals which traverse the whole polypi- 

 dom. The polyps, which are distributed over the whole surface, can 

 withdraw into the cavities ; they are, besides, of an extremely vital 

 sensibility : the least shock impresses itself on the tentacula, the 

 impulse of a wave even producing contraction; in response, the 

 animal, which is well developed, sallies out perceptibly, but imme- 

 diately retires again to hide itself in the cell. 



We find on the coast, in the Channel, and in the North Sea, 

 Alcyonium digitatum, the mass of which is of a reddish white, 

 ferruginous, or orange ; A. stellatum, found on the shores of the 

 Mediterranean, is expanded in its upper part, narrow towards its base, 

 very rough on the surface, and rose-coloured ; A. palmatum is cylin- 

 drical, branching at the summit, of a deep red, except at the base, 

 where it is yellow : this is met with in the Mediterranean. 



We may note as a type, altogether different from any yet touched 

 upon, the Nepktys, in which the polypidom is a coriaceous tissue 

 bristling with spiculae over its whole surface. In N. Chabroli, the 

 polypidom is squat, with thick spreading arms covered with lobiliform 

 branches, the tubercular polypidom of which are columnar and obtuse, 

 the sicula green, and the tentacula of the polyps yellow. 



" On a cursory view," says Dr. Johnston, " the polypodium of the 

 three families embraced appear very dissimilar, and accordingly, by 

 many recent authors, they have been scattered over the class, and 

 placed widely asunder. The affinity between them, however, is gene- 

 rally acknowledged, and had been distinctly perceived by some of the 

 earliest zoophytologists. Thus Bohadsch found so much in common 

 in the typical pennatulae and a species of Alcyonium, that he has not 

 hesitated to describe them as members of the same genus ; and, 

 although the more systematic character of Pallas prevented him from 

 falling into this error, if error it can be called, he did not the less 

 recognize the relationship between the genera or families. Pallas also 



L 



