MADREPORARIAN CORALS 43 



exist laminae of calcium carbonate — called the dissepiments 

 — which pass transversely across the inner septal spaces in 

 the depths of the calyx, shutting off the upper spaces where 

 the living polyp tissues are found from the dead coral below ; 

 and in some cases true tabulae occur. In this respect the 

 calices of Lophohelia approach in structure the calices of the 

 next family of corals — the Astraeidae — whereas Amphihelia, 

 in retaining the open spaces between the septa right down 

 to the base of the calyx, resembles the Turbinoliidae and the 

 other genera of the Oculinidae. 



There is, however, so much variation in all these char- 

 acters in both genera, that it is sometimes difficult to deter- 

 mine without most careful examination whether a given 

 specimen is an Amphihelia or a Lophohelia. This difficulty 

 is increased by the frequent occurrence in specimens obtained 

 from some localities of the natural grafting of the two genera. 

 Specimens are found of which one branch may be a true 

 Lophohelia and the others Amphihelia, and when the place 

 where the branches join is carefully examined, even in 

 sections, no boundary line can be distinguished to indicate 

 where the Lophohelia tissue begins and where the Amphi- 

 helia tissue ends (Fig. 13). Such grafts might readily lead 

 to a hasty but probablv erroneovis conclusion that the two 

 forms are not distinct, but are only environmental variations 

 of the same genus and species. 



It is not known how this grafting takes place, but as 

 de Lacaze-Duthiers ^ remarks : "La puissance blasto- 

 genetique est des plus actives dans cette espece {i.e. Auiphi- 

 hclia oculata). Tout ce qui touclie a une partie du zoantho- 

 deme vivant est fixe, retenu et reconvert par le sarcosome 

 d'abord, et plus tard par le tissu sclereux." Worms, molluscs, 

 bryozoa, and other living things are caught, enveloped by 

 the soft coenosarc, and subsequently covered by the hard 

 coenosteum, and it seems probable, therefore, that when a 

 Lophohelia larva settles on a branch of Amphihelia, or vice 

 versa, and begins to grow, the base of the young colony 

 becomes, in like manner, entirely submerged in the growing 



1 H. de Lacaze-Duthiers, " Zoanthaires sclerodermes," Arch. Zool. 

 Expev., 3", v., 1897, p. 143. 



