32 



CORALS 



Group B. — Polyps with twelve mesenteries. 



Family 6. Seriatoporidae. 

 Family 7. Madreporidae. 



These families include most of the recent Madreporarian 

 corals, but there are still some recent corals, such as Pyro- 

 phylha, (iuynia, Bathyactis, etc., and many fossil corals 

 which cannot, at present, be placed in any of them. 



Before proceeding to a systematic description of a few 

 representative genera of each of these 

 families it is necessary to refer briefly 

 to the arrangement of the mesenteries 

 of the Madreporarian polyps and their 

 relation to the septa. 



It has been found that in the 

 development of the Madreporarian 

 coral polyp there is a stage when 

 there are twelve mesenteries, and 

 that these twelve mesenteries have 

 certain definite characteristics. 



The mesenteries are thin laminae 

 of soft fleshy substance passing from 



cnteries (protocnemes) ; DS, i\^q body Wall tO the StomodaCUm Or 

 the directive septa ; St, the c ^ 



throat. Some of these reach the 

 stomodaeum, others do not. 



From each end of the stomodaeum, 

 which is sometimes round and some- 

 times oval in section, a pair of mes- 

 enteries pass to the body wall, called the Directive mesenteries 

 (Fig. 6, III-IV), and in each lateral space between the pairs 

 of directive mesenteries there are four mesenteries, making 

 a total of twelve in all. 



These mesenteries are called the Primary mesenteries or 

 Protocnemes, and it may be added they are formed in bi- 

 lateral pairs, that is to say, at the time of their appearance 

 one member of a pair corresponds with the other member 

 on the opposite side of the stomodaevmi. The order of 

 sequence of these mesenteries is indicated by the numbers 

 I-VI in the diagram. 



Fig. 6. — Diagram of a 

 transverse section of a 

 Madrcporid calyx to show 

 the relation of hard parts 

 (thick lines) and soft parts 

 (thin lines). I-VI, the mes- 



stomodaeum ; III-IV, the 

 directive mesenteries. On 

 the right side of the diagram 

 the section is taken through 

 the stomodaeum ; on the 

 left, below it. 



