370 COELENTERATA ANTHOZOA chap. 



Nearly all the zooids and even the colonies of the Zoantharia 

 are unisexual, but some species, such as Manicina areolata 

 (Wilson), Meandrina labyrinthica (Duerden), Cerianthus mem- 

 branaceus, and others, are hermaphrodite. Mr. J. S. Gardiner has 

 recently given reasons for believing that the genus Mabellum 

 is protandrous. 



Skeleton. — The soft tissues of the Zoantharian zooids may 

 be supported or protected by hard skeletal structures of various 

 kinds. In the Zoanthidea and the Actiniaria there are many 

 species that have no skeletal support at all, and are quite naked. 

 These seem to be sufficiently well protected from the attacks of 

 carnivorous animals by the numerous nematocysts of the 

 ectoderm, and perhaps in addition by a disagreeable flavour in 

 their tissues. Anemones do not seem to be eaten habitually by 

 any fish, but cases have been described of Peachia hastata being 

 found in the stomach of the Cod, and of Udwardsia in the 

 stomach of the Flounder.^ On the Scottish coasts Anemones are 

 occasionally used with success as a bait for cod.^ The body- 

 wall of Udwardsia, however, is protected to a certain extent 

 by the secretion of a mucous coat in which grains of sand and 

 mud are embedded. Some Anemones, such as Uriicina, Peachia, 

 and others, lie half-buried in the sand, and others form a cuticle, 

 like that of Pdwardsia, to which foreign bodies are attached. 



Cerianthus is remarkable for constructing a long tube com- 

 posed of a felt-work of discharged nematocysts mixed with mud 

 and mucus, into which it retires for protection. In the Zoanthidea 

 the body-wall is frequently strengthened by numerous and 

 relatively large grains of sand, which are passed through the 

 ectoderm to lie in the thick mesogloea. 



In the Madreporaria a very elaborate skeleton of carbonate of 

 lime is formed. In the solitary forms it consists of a cup-shaped 

 oater covering for the base and column of the zooid called the 

 " theca," of a series of radial vertical walls or " septa " projecting 

 into the intermesenteric chambers carrying the endodermal 

 lining of the coelenteric cavity with them, and in some 

 cases a pillar, the " columella," or a series of smaller pillars, the 

 " pali " projecting upwards from the centre of the base of the 



' M'lutosh, "The Marine Invertebrates and Fishes of St. Andrews," 1875, pp. 

 37, 38. 



2 M'Intosh, "The Resources of the Sea," 1899, pp. 10, 129. 



