MADREPORARIAN CORALS 67 



the whole of the under surface of the coral, in a healthy 

 specimen. 



The mouth leads into a short stomodaeum or throat, and 

 between the throat and the body wall there are as many 

 mesenteries as there are septa. The pair of mesenteries 

 situated at the angles of the mouth, one mesentery on each 

 side of the directive septa, are the directive mesenteries. 

 The other mesenteries are situated between the lateral septa 

 and are either complete or incomplete, the primary and 

 secondary mesenteries extending the whole distance from 

 the margin to the throat, the others extending only a part 

 of the distance from the margin to the throat, according to 

 the series to which they belong. In the lower parts of the 

 disc the mesenteries are perforated by the synapticula. 



It will be seen from the account given above that the 

 polyp of a Fungia is an ordinary Madreporarian polyp and 

 presents no feature of an extraordinary kind except its great 

 size and the perforation of the mesenteries by the synapticula. 



The colour of the polyps is very variable, some specimens 

 being described as green and others as brown, but the inflated 

 tips of the tentacles are white. 



No account of the structure of Fungia would be satis- 

 factory without reference to some of the principal variations 

 from the types that have been described. 



On some reefs the symmetrically round disc shape is 

 rare, most of the specimens being elongated in the directive 

 diameter so as to become, oval. Other variations may be 

 found in which the fossa is not elongated but an almost 

 circular pit, or the upper surface very convex or the outline 

 quite irregular. In some specimens the thecal wall as seen 

 between the costae is perforated.^ 



Variations in colour have already been referred to, but 

 there seems to be also some difference between species or 

 perhaps simple variations in the length of the tentacles. 

 Rumphius refers to them as little blisters (" blaasjes "), and 

 Dana says the tentacles are small and rudimentary, but the 

 excellent photographs of the living polyp by Saville Kent, 



1 specimens showing an imperforate thecal wall were formerly placed 

 in a separate genus Cycloseris. 



