154 On the Morphology of the Madreporaria. 



witliout involvinfr tlie parent stomodaeum — tliat !«!, a bud may 

 appear on the oral disk, and from ihe bec^inninfi^ remain as a 

 distinct individual, as r gards its mesenteries and stomodaium, 

 just as in the case of buds arising on the column-wall. In 

 the partly diagrammatic representation of a transverse section 

 of a bioral polyp of C. arbusctila, given in tig. 7, two appa- 

 rently distinct polyps are enclosed within one column-wall, 

 wiiich was terminated by a single system of tentacles. The 

 larger polyp to the right is normally hexamerous, with two 

 pairs of directives, while the smaller to the left is still im- 

 perfect, and on its inner side is wantinor a pair of directives. 



I regard the small polyp as a bud which has arisen on the 

 disk of the larger polyp, but, on account of its closeness to 

 the parent polyp on the inner side, the development of the 

 mesenteries has not proceeded symmetrically. It must be 

 admitted, however, that it is difficult to distinguish between 

 a new mesenterial system arising indej)endently on the disk 

 of another polyp, and one wiiich has developed as an integral 

 part of a polyp, and been pinched off later. 



Summar'i/. 



a. The polyps in Madreporaria which arise asexually 

 by budding are new individuals, with all the charactrristics 

 of hexamerous cyclical polyps reared directly from larvse; 

 whereas in asexual reproduction by continuous tission no 

 new polyps are ever formed. 



b. On any gemmiferous colony a few polyps frequently 

 occur which are much larger than the usual adult form. The 

 additional mesenteries and septa of these, as observed in the 

 genera Forites, Madrepora, Cladocora, Stephanoccenin , Sj/en- 

 ostrcea, and Vculina, do not continue the hexameral cyclic 

 plan of the polyp, but conform in character with the mesen- 

 teries and septa alieady present, and include one or two 

 additional pairs of directives. 



c. In Mudrepora and Forites the new mesenteries arise as 

 complete or incomplete bilateral pairs within one or both of 

 the directive entocceles; but in Cladocoro, Stephanoccenia, 

 JSohnostraa, and Oculina they arise as unilateral isocnemic 

 pairs within one or more exocoelic chambers. 



d. Fission of the enlarged polyps takes place in such a 

 wa}' that each of the two moieties resembles an ordinary bud 

 or larval polyp ; each conforms \\ith the hexameral plan, and 

 is provided with two pairs of directives. 



e. Fission in gemmiferous corals is morphologically distinct 

 from the same process in fissiparous corals, for in the latter- 



