5S I 



ANTHOZOA 



75 



^^|l|e slit-like or oval fissure of the mouth. The oral disk is furnished with a ring 

 of tentacles round its margin, and opeiis into a membranous oesophageal tube 

 conducting into the gastric cavity. The outer covering of the body, the parts 

 of which are designated as wall, oral disk, and pedal disk, are constituted of 

 ectoderm and entoderm, between which is a thin layer of mesoderm (mesogloea). 

 Six, eight, or more radially disposed vertical partitions (mesenteries), (Figs. 94, 

 95), projecting inwardly from the body-wall, divide the gastric cavity into a 

 series of radiating compartments (mesenteric pouches). The mesenteries are 

 continuous upwardly with the hollow, muscular tentacles ; while the generative 

 Organs are attached to their faces near the lower end of the body. The 

 mesenteries are »covered on both sides with muscular tissues, and bear mesen- 

 teric filaments on their curled inner edges. On one side of the mesenteries 

 the muscle fibres are transversely directed, on the other longitudinally. The 

 longitudinal System is usually considerably folded and thickened ; and the 

 disposition of these 

 muscular portions is of 

 great importance from a 

 systematic standpoint, 

 since it reveals the 

 bilateral symmetry of 

 many Anthozoans, and 

 enables one readily to 

 identify the antimeres. 

 If a polyp individual be 

 cut in two by a plane 

 passing through the 

 longer axis of the 

 mouth-opening, then, in 

 the Octocoralla (Fig 

 94), the mesenteries of 

 the right half will have 



all the muscular thickenings disposed on the right-hand side, and those of the 

 left on the left-hand side. In the Hexacoralla (Fig. 95) the mesenteries are 

 grouped in pairs, with the muscular thickenings of any pair facing each other. 

 Two pairs, however (those corresponding with the opposite extremities of the 

 longitudinal mouth), form often an exception to this rule, since these have the 

 muscular thickenings placed on opposite sides. These are called the directive 

 mesenteries, and serve to indicate the longitudinal axis of the body. 



Only a few Anthozoa have permanently soft bodies ; the majority secreting 

 calcareous, horny, or partly horny and partly calcareous structures, termed the 

 skeleton or corallum. The simplest form of corallum is that composed of 

 microscopic, round, cylindrical, acerate, or tuberculated spicules of carbonate 



Fig. 94. 



Diagrammatic section of 

 the soft parts of an Octo- 

 coralla (Alcyoninm). x, Oeso- 

 phagus ; 1, 2, 3, 4, Mesen- 

 teries of the left side (after 

 R. Hertwig). 



Fig. 95. 



Diagrammatic section of the soft parts of 

 a Hexacoralla. In the upper half (above the 

 line a — h) the section passes through Oeso- 

 phagus s ; in the lower half, beneath the 

 same. Corallum indicated by heavy lines. 

 r, directive mesenteries. 



Morphology of the Madreporaria. A series of papers in Ann. and Mag. Nat. Hist., ser. 7, vols. ix., 

 X., xi., xvii.,xviii. (1902-1906), and Biol. Bull.,vols. vii. and ix. (1904-1905).— /rfew, Recent Results on 

 the Morpliology and Development of Coral Polyps. Smithsonian Miscellaneous Collections, Quart. Lss., 

 1904, vol. xlvii. — Felix, J., Die Anthozoen der Gosan Schichten in den Ostalpen. Palaeontographica, 

 1903, vol. xlix. Nuinerous other papers, especially in Zeitsch. deutsch, geol. Gesellsch. — Caimthers, 

 R. G., The primary Septal Plan of the Rugosa. Ann. and Mag. Nat. Hist. 1906, ser. 7, vol. xviii. — 

 Gordon, O. E., Studies on early Stages in Paleozoic corals. Am. Jour. Sei., 1906, vol. xxi. — Bnrwn, 

 T. 0., Studies on the Morphology and Development of certain Rugose Corals. Ann. N.Y. Acad. Sei., 

 1909, vol. xix. 



