﻿102 SMITHSONIAN MISCELLANEOUS COLLECTIONS [VOL. 4/ 



complete by reaching as far as the stomodseum. It is found, how- 

 ever, that in the later stages the mesenterial increase rarely proceeds 

 equally all round the polyp. Fission of one or both of the two 

 stomodsea may now take place, perhaps with a variable number of 

 mesenteries attached to each moiety; the same process is continued, 

 the incomplete mesenteries in turn become complete, and new pairs 

 are developed, but additional directives are never formed. In every 

 case the fission plane is within two entocceles. 



Examination of parts of the polypal system of mature fissiparous 

 corals, such as species of Isophyllia, Mceandrina, and Favia, fully 

 confirms the results from the early fission stages of other forms. 

 The mesenteries, septa, and tentacles are not disposed in ordinary 

 cycles, no hexamerism or other regular arrangement is determinable, 

 and directive mesenteries are absent. The important conclusion is 

 thus reached that a fissiparous coral, however large, morphologically 

 represents but one complex individual polyp, having many oral 

 apertures and the mesenteries in separate stomodaeal systems ; on the 

 other hand, a gemmiferous colony is constituted of numerous dis- 

 tinct individuals, practically all alike. 



A third, somewhat intermediate form of non-sexual increase some- 

 times occurs. On most gemmiferous colonies certain polyps are 

 found which are much larger than the others, growing to as much 

 as double the usual size, and among them are various stages leading 

 to division into two daughter polyps. They suggest that the polyps 

 are undergoing ordinary fission, for which reason it has been assumed 

 that both gemmation and fission may occur on one and the same 

 colony. An anatomical examination of many such enlarged polyps 

 reveals, however, that they are not instances of true fission as above 

 established. The resulting moieties are found to be really new in- 

 dividual polyps, having two pairs of directives and cyclic hexamerism, 

 just as in polyps arising in the ordinary way as buds or from larva;. 

 This is clearly shown in figure 16, representing a section through an 

 enlarged polyp of Cladocora arbuscula in process of fission. In the 

 living condition the whole polyp was surrounded by a single column 

 wall, and provided with a single tentacular system and a bioral disk. 

 Manifestly fission is taking place across the median plane, and, when 

 completed, each half will represent a distinct hexamerous Cladocora 

 polyp, comparable with others arising as ordinary buds. 



The growth of these enlarged polyps has been followed step by step 

 on several different species of Madrcpora, Poritcs, Solenastraa, and 

 Oculina. It is found that new pairs of mesenteries are added to an 

 ordinary polyp without increasing the number of cycles, and that in 



