CORALS. 



121 



divided into two individuals, both of which have a common stomach and a common 

 basal attachment. The complete fission or division of the original individual into two 

 isi accomplished in the last stage, which is one in which we have the same common 

 base of attachment, bearing at its top two perfect individuals, which have resulted from 

 the self-division of the single animal with which we started. 



Okdee II. — HALCYONOIDA. 



The second large group of Actinozoa is called the Alcyonoida or Halcyonoida from 

 the genus JTalcyonium, supposed to be the nest of the " Halcyon " or king-fisher 

 of the Greek fables. To this division belong the "sea-fans" and "sea-whips," 

 so-called, and many others, some of which are widely aberrant in general char- 

 acters. So different in structure from the typical " sea^-f ans," are many of the genera 

 now thrown among the Halcyonoids, that they are probably destined later, when a 

 more perfect classification is made known, to be the nuclei of new groups of equal 

 rank. 

 , The colonies of Halcyonoids have commonly a branching form, are flattened in fan- 

 like shapes or extended into long, flexible whips. In Tuhipora, or the organ-pipe coral, 

 we have the hard parts tubular in shape. The amount of deposition of solid matter in 

 their tissues varies considerably. In certain genera all hard inorganic depositions are 

 wanting, and the body is soft and without skeleton. In still others, secretions in the 

 form of spicules are well developed. 

 Of those which have a hard skele- 

 ton, we find all degrees of hard- 

 ness, from a simple horn-like axis 

 of the " sea-whips," to the extreme 

 hardness of the ornamental coral 

 of commerce. 



In the classification of the Hal- 

 cyonoids many systems have been 

 attempted, but the subject is still 

 in an unsatisfactory condition, and 

 at present there is little uniformity 

 among naturalists in regard to the 

 limits of families and genera. A 

 well-marked genus called Antip- 

 athes is separated from the Hal- 

 cyonoids by almost universal con- 

 sent, as the family Am^tipathaeia, and seems to stand between the Actinoids and the 

 group which we are now considering. The likeness of Antipathes to the sea-fans is 

 best seen in the branching character of its axis, while the number of tentacles and the 

 absence of side branches to these organs, ally it more closely to the majority of the 

 Actinoids. One of the most interesting species of Antipathes is the well-known A. 

 columnaris. In this species we have a very interesting case of a worm building a 

 tube from the smaller lateral branches of the coral or by its presence causing a modi- 

 fication in the mode of growth of the coral. Upon one side of the axis of the Anti- 

 pathes, the worm, a true annelid, places itself, and the small lateral branches of the 

 axis in the immediate neighborhood are modified into a columnar network forming the 



Fig. 116. — Section of red-coral. 



