MORPHOLOGY OF THE CORAL SKELETON. 37 



be doubted that at first all corals possessed a basal plate. It seems that in 

 some corals it has been suppressed, and the formation of the skeleton begins 

 with the building- of the septa. Such a condition has been described by 

 Lacaze-Duthiers for Balanophyllia. ^ 



THE EPITHECA. 



The discussion of the epitheca can best be introduced Ijy another 

 quotation from von Kochr "The epitheca is secreted by the outer sur- 

 face of the pallium and is, as this passes directly into the foot, a continua- 

 tion of the basis (basal plate), and is separated therefrom in that it does 

 not rest upon an object of sui)port (Unterlage), but makes an angle with 

 this (which may regarded as a plane)." The epitheca is a coating laid 

 down on the outside of the corallum over the ends of the septa and costaj 

 and on the outside of the wall. It presents numerous conditions; it may 

 be transversely wrinkled, covering the whole outer surface of the corallum; 

 it may be highlv polished, or it may be present as occasional threads or 

 shreds encircling some coralla at various levels. The height to which the 

 epitheca rises on the outside of the corallum is usually considered to be an 

 indication of the distance the soft parts extended down the outside of the 

 corallum. (See PI. I, fig. 1.) If the polyp invested the whole corallum, 

 there would be no epitheca; if, when distended, it reached almost to the 

 base, there would l^e only a little epitheca; if the animal did not protrude 

 itself beyond the calicular cui), the epitheca would reach to the calicular 

 margin — the epitheca keeping pace in its growth with the gradual eleva- 

 tion above the base of the lower edge of the soft parts of the animal. To 

 how great an extent this is proved I am not prepared to say. Ogilvie* says: 

 "The epitheca is an external basal structure laid down at the angle of the 

 aboral wall, where it bends toward the oral or peristomal region of the 

 polyp" (figs. 22, 36). Moseley has proved, from species of Flabellum 

 collected during th(! Challenger Expedition, that the soft parts do not extend 

 beyond the edge of the cup.* This fact may be correlated with the 

 epitheca extending to the upper edge of the corallum.^ 



1 Arch. Zool. Exp., .Sd ser. Vol. V, 1897. I bave been unable to consult this paper, and base my 

 reference to it on Bernard's paper in Jour. Linn. So(^, London, Zool., Vol. XXVI, 1898, p. 512. 



-Op. Blip, cit., p. 254. 



'Micros, and Syst. Stud. Mad. Types of Corals, p. 2^8. 



■•Deep sea corals: Challenger Reports, p. Ifi2. 



"Fowler thinks that the polyp <>f FlnheUum patagonicum, when fully distended, covers the upper 

 fourth of the outside of the corallum. (.Minrt . .lour. Microsc. Sci., Vol. XXV, October, 1885, p. 586. 



