ALCYONOID POLYPS. 81 



crimson or purple shade. Dun colors also occur, as ash- 

 gray, and dark brown, and almost black. Some kinds, the 

 Sponggodiae, are too flexible to stand erect, and they hang 

 from the coral ledges, or in the coral caves, in gorgeous clus- 

 ters of scarlet, yellow, and crimson colors. 



The species of this order spread from the tropics through 

 the colder seas of the globe, and occur at various depths, down 

 to thousands of feet. 



The two following are the most striking external peculiari- 

 ties of the polyps : the number of tentacles is always eight ; 

 and these tentacles are always fringed with papillae, though the 

 papillae are sometimes mere warts. Some of the various forms 

 of the polyps are shown in the figures on the following pages. 



But besides these characteristics, there is also the follow- 

 ing : the existence of only eight internal septa, and these septa 

 not in pairs ; consequently, the interior is divided into only 

 eight compartments (octants), and with each a tentacle is con- 

 nected. Hence in the Alcyonoids, as Prof. Verrill has ob- 

 served, the areas externally, and the compartments within, 

 are all amhulacral, or tentacular, which makes a wide dis- 

 tinction between them and the Actinoids (p. 28) in which only 

 the alternate are tentacular. 



The solid secretions of these polyps are of two kinds : Ei- 

 ther (1), internal and calcareous ; or (2), epidermic, from the 

 base of the polyp. The latter make an axis to the stem or 

 branch, which is either horney (like that, in Antipathus, p. 62) or 

 calcareous. A few species have no solid secretions. 



All the species are incapable of locomotion on the base ; 

 yet there are some that sometimes occur floating in the open 

 ocean. 



The three following divisions of the Alcyonoids are those 

 now generally recognized : 



