496 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



conditions. 1 recognize vegetative growth only by budding and by fission. The differences 

 manifested within each division are mainly such as are dependent upon the position and method 

 according to which the process takes place, and these do not in any way modify the essential 

 distinctions between the two types. 



When studying the mesenteries of adult polyps, two great divisions were determinable. 

 In one section, including the genera. Orbicella, Solenastrsea, Oculina, Oladocora, Astrangia, 

 Phyllangia, and Siderastrsea, the mesenteries of all the polyps in a colony were found to be 

 arranged according to the regular, hexameral. cyclic plan, with two pairs of directives; while in 

 the other section, embracing the genera Faritt, Diehacwnia, hoplnjUta, Municina, Mn'tinrfrhia, 

 and Colpophyllia, the mesenteries have lost their hexameral cyclic regularity, including the 

 directives, and little more than a distinction into complete and incomplete pairs can he established. 

 It was further found that the first-mentioned group comprises genera whose asexual growth is by 

 gemination, while fissiparity is characteristic of the latter. In whatever position the buds are 

 produced, whether on the disk, upper part of column wall, intercalary, marginal, apical, 

 ccenosareal, or stolonic, matters not; the polyps retain a hexameral disposition of the organs. 

 Also, whether the products of fission assume an individuality, or remain as constituents of a 

 complicated system, makes little difference as regards the irregularity of the arrangement of the 

 mesenteries, tentacles, and septa. 



This fundamental difference in the adult polyps of the two groups seems to be determined 

 by the fact that in gemmation the polyp as a whole is formed practically as a new individual, 

 whereas, in fissiparity, some parts at least of the essential organs of the new polyp are obtained 

 fully formed from a parent polyp. In the one case the polyp as a whole is free to develop 

 according to a definite plan characteristic of the species, while in the other new organs are to be 

 added and adapted to parts already formed, and fissiparity may again take place before any 

 second regularity has been established. Growth in the one is altogether new, and in the other 

 it is patchwork — some regions new, some regions old. 



It has not been possible to determine whether in every case of gemmation the mesenteries are 

 formed wholly independent of those of the parent. In some instances they certainly are, and in 

 others it seems very probable. In very young buds the mesenteries are already found to be 

 wholly cut off from those of adjacent polyps, and the bud is free to develop as symmetrically 

 as any sexually-produced polyp. 



Either one or the other method of growth is in the main characteristic of any species; 

 sometimes a case of simple fissiparity may be found in a species where gemmation prevails, as in 

 Madrepora and Parties, but the converse has never been found — that is, the production of buds 

 where fissiparity is the ride. 



Intermediate stages are not wanting which seem to indicate how the passage from the one mode 

 of colonial growth to the other has been brought about. In corals like Oladocora and Oculina 

 the buds usually arise toward the upper extremity of the column wall, and it is easy to understand 

 how gemmation may overstep, as it were, the usual boundary and occur on the discal wall. Such 

 apparently happens, for occasionally polyps of C arbuscula and 0. diffusa are found in which 

 two oral apertures are inclosed within one system of tentacles, and a common column wall and 

 theca occur. In such cases the two polyps may be equal, or one may be larger than the 

 other. Microscopic examination of these shows that the normal hexameral regularity of one of 

 the polyps, along with the presence of two pairs of directives, has in no way been disturbed, and 

 the other polyp is either perfectly hexameral. or evidently on the way to become so. Such double 

 polyps can certainly not be regarded as fission products, at any rate not according to the plan 

 followed where fissiparity prevails. They seem best understood as discal buds, or as examples 

 of fissiparous gemmation (see foot-note). 



It is but one step from discal budding to oral fission, or perhaps the conception may be 



"The occasional instances of simple fission in corals reproducing by gemmation have since been found to be a 

 modified form of budding, which I have termed " Fissiparous Gemmation " ; the products are altogether different 

 from those in ordinary fissiparous growth, being cyclical, hexamerous polyps, with two pairs of directives. This 

 discovery greatly strengthens the separation between the two groups of corals. "Morphology of the Madre- 

 poraria. — IV. Fissiparous Gemmation." Ann. Mag. Nat. Hist. (In press.) 



