CLASSIFICATION OF CCELENTERA. 157 



II. Sub-class Anthozoa, or Actinozoa 



Polypoid forms with well developed gullet and septa, and cir- 

 cu moral tentacles. 



(i.) Zoantharia or Hexacoralla. 



(a) Actiniaria. Sea anemones. 



Actinia, Anemonia, Tealia, Cerianthus. 



(b) Madreporaria. Stone .or reef corals. 



AstrcBa, Madrepora, Fungia, Mcmndrina. 



(c) Antipatharia. " Horny " black corals, with an axial 



skeleton, and occasional dimorphism between 

 nutritive and reproductive "persons," Antipathes. 

 (2.) Alcyonaria, or Octocoralla. 



Alcyonium (Dead men's fingers), Tubipora (Organ pipe 

 coral), Coral Hum (Red coral), Gorgonia, Pennatula 

 (Sea pen), Monoxenia (non-colonial). 



The Rugosa, or Tetracoralla, include extinct, or almost entirely extinct, 

 forms, with numerous septa in some multiple of four. 



C. Class CTENOPHORA. 



Delicate free swimming organisms, generally globular in form, moving 

 by means of eight meridional rows of ciliated plates, or comb-like com- 

 binations of cilia. The stinging cells are usually modified into "adhesive 

 cells." The mouth is at one pole, and leads into an ectodermic gullet. 

 The gastric cavity is usually much branched. The mesenchyme is very 

 well developed, and includes muscular and connective cells. At the 

 aboral pole there is a sensory organ, including an " otolith," which seems 

 of use in steering. Here, also, there are two excretory apertures. Ex- 

 cept in Beroe and its near relatives, there are two retractile tentacles. 

 All are hermaphrodite. The development is direct. They are pelagic, 

 very active in habit, carnivorous in diet, and often phosphorescent. 

 According to Lang, they have affinities with Planarian "worms," but 

 this is very uncertain. 

 Examples : 



(a) With tentacles, Cydippe and the ribbon shaped Venus' Girdle 

 (Cesium Veneris}. 



(b} Without tentacles, Beroe. 



History. Of corals, as we would expect, the rocks preserve a faithful 

 record, and we know, for instance, that in the older (Palaeozoic) strata, 

 they were represented by a distinct series (Rugosa or Tetracoralla), of 

 which we have at most two or three survivors. We often talk of the 

 imperfection of the geological record, and rightly, for much of the 

 library has been burned,' many of the volumes are torn, whole chapters 

 are wanting, and many pages are blurred. But this imperfect record 

 sometimes surprises us, as in the quite distinct remains of ancient 

 jelly fish, which animals, as we know them now, are apparently little 

 more than animated sea water. We should also grasp the conception, 

 with which Lyell first impressed the world, of the uniformity of natural 

 processes throughout the long history of the earth. Thus in connection 

 with Ccelentera we learn that there were great coral reefs in the incalcul- 



