30 CORALS 



tion, reference may be made to the polyps of one of the 

 colonial corals that has just been described and their rela- 

 tion to the corallum. 



The polyps of Lophohelia, according to de Lacaze- 

 Duthiers, are provided with a crown of tentacles of various 

 lengths corresponding in number with the septa (about 

 twenty in a full-grown polyp) ; the mouth in the centre of 

 the disc is slit-shaped, the slit being parallel with the axis 

 of the branch. The outer wall of the polyp flows over the 

 rim of the calyx, and is continuous with a thin laver of 

 fleshy substance that covers the coenosteum and brings 

 the polyps into organic continuity with one another. This 

 communal lining substance may be called " Coenosarc." 



In life the polyps and the coenosarc are so remarkably 

 transparent that the details of the coral structure can be 

 seen through them, but nevertheless they do exhibit a faint 

 yellow or orange colour, which is accentuated on the disc 

 round the mouth. The tentacles are also transparent and 

 faintly yellow in colour, dotted with little white spots, and 

 terminating in a white conical point. All these soft parts 

 of the Lophohelia colony are situated above the hard parts 

 — there are no canals or other living tissues that penetrate 

 into the coenosteum or into the septa or walls of the calices, 

 and consequently, when the colony dies, the coenosarc peels 

 off the coenosteum and the polyps become detached from 

 their calices. 



This is in marked contrast to what is found in perforate 

 corals in which both polyps and coenosarc are firmly locked 

 into the corallum by canals and strands of tissue that pass 

 through the perforations. 



The classification of the Madreporarian corals is still in 

 a very unsatisfactory and unsettled condition, owing, in 

 part, to the very limited knowledge we possess of the 

 structure of the coral polyps, and in part to the wide range 

 of structure that the group exhibits leading to interdigita- 

 tion of the families and sub-orders. 



In some of the Madreporaria, such as the genera Madre- 

 pora itself, Porites, Pocillopora, and Seriatopora, the polyps 



