58 CORALS AND CORAL ISLANDS. 



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 peculiarities 

 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 following : 

 the existence of only eight internal septa, and these septa not 

 m pairs; consequently, the interior is divided into only eight 

 compartments (octants), and with each a tentacle is connected. 

 Hence in the Alcyonoids, as Prof. Verrill has observed, the 

 areas externally, and the compartments within, are all ambu- 

 lacral, or tentacular, which makes a wide distinction between 

 them and the Actinoids (p. ii) in which only the alternate are 

 tentacular. 



The solid secretions of these polyps are of two kinds : Either 

 (i), 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 horny (like that in Antipathus, p. 42) or cal- 

 careous. 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 : — 



I. The Alcyo?iiu7n tribe, or Alcyonacea. — One of the forms 

 under this tribe is represented in the annexed figure. It is 

 from the Feejees (like most of the zoophytes figured by the 

 author), and in the living state the polyps had the middle por- 

 tion of the tentacles pale brown, with the fringe deep brown. 

 In another more beautiful species of the genus, from the same 

 region, the Xenia fioi'ida D. (made Xenia Dance by Verrill, as 

 it proved to be distinct from Lamarck's species to which the 

 author referred it), the polyps are as large, but shorter, and the 

 colour is a shade of lilac. These species differ from the larger 



