MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 539 



L865) and Eunth (1869-70), and is regarded by Neumayr (1889) as a characteristic of the 

 highest morphological significance. The bilaterality in many forms is only clearly developed in 

 the early stages, but the external surface of corallites often exhibits pinnate streaks or ridges 

 which correspond with the internal septa, and these demonstrate conclusively the bilateral manner 

 in which the septa have arisen, e. g., Streptelcisma, Zaphrentis. 



In the Cyclocnemaria the mesenteries are as a rule arranged in two or more regular cycles, 

 while in the Entocnemaria they are in one cycle only, with merely alternately large and 

 small members. In the absence of any knowledge of the soft parts of a coral we may assume 

 that in general the septa of the former group will be polycyclic, while those of the latter will be 

 monocyclic or at most dicyelic. Where asexual reproduction by incomplete discal fission prevails, 

 there is a tendency toward the dicyelic condition, but these forms can be readily distinguished 

 from the Palaeozoic types with merely large and small alternating septa. 



With regard to the further employment of the mesenteries and septa of Madrepoiaria for 

 taxonomic purposes, the wide differences in the arrangement and nature of these organs in 

 gemmiferous and fissiparous genera may now be considered. In mature polyps of the former it 

 has been found that a cyclical regularity prevails, and two pairs of directives are always 

 present, hut in the latter the introduction and continuance of fission carries with it marked 

 changes, not only in the mesenteries, hut also in the septa and tentacles. No other polypal 

 characteristic seems to exert such a profound influence upon the nature of the compound coral 

 as a whole. Hut by no means can the results of fission lie regarded as of such fundamental 

 significance as those distinguishing the Entocnemaria and Cyclocnemaria. The young polyps of 

 both gemmiferous and fissiparous genera are built upon exactly the same plan, and it is only with 

 the advent of vegetative reproduction that they become divergent. 



Fissiparity would appear to he a condition which may arise in any group of corals, and its 

 occurrence docs not necessarily indicate any natural relationship among the forms in which it 

 prevails, in any classificatory scheme it can probably be regarded as only of subfamily impor- 

 tance, which is practically the position assigned it by Duncan." In this case the divisions, in 

 whatever families they occur, may lie defined as follows: 



Gemmantes. — Asexual reproduction takes place by gemmation, and each polyp represents a 

 distinct individual. The tentacles, mesenteries, and septa are arranged in alternating cycles, and 

 two pairs of directive mesenteries are present in each polyp. 



Wissiparantes. — Asexual reproduction takes place by stomodaeal fission, without the production 

 of morphologically complete polyps. The tentacles, mesenteries, and septa, after fission i- estab- 

 lished, arc not arranged in regular alternating cycles, and no new directive mesenteries arise. 



The arrangement and form of the tentacles in the Madreporaria can not attain that 

 systematic value which they possess in the Actiniaria. In the latter the origin of one or more 

 tentacles from a single mesenteric chamber is a character of much importance, and affords a 

 means of dividing the Hexactinhe into the two suborders Actinimv and Stichodactylinse. In the 

 corals no instance of the stichodactylinous condition has been met with, and any other tentacular 

 characteristic so far disclosed seems worthy of only generic, rarely of family, recognition. With 

 the exception of the bifurcated entoaelic tentacles in the single genus Siderastrsea, the organs 

 are invariably simple in corals. As a rule they are arranged in close, alternating, entaemseous 

 cycles, but in the Fungidffi the cycles are distant and tend to lose their regularity of disposition. 

 The prevalence of the knobbed or swollen tentacular apex in corals is noteworthy, considering 

 how rarely it occurs in the Actiniaria (e. g. . Corynactis, Ricordea, CoraZlimorphus). Tentacular 

 introversion is probably very general throughout the Madreporaria. but rare among the 

 Actiniaria. 



The sphincter muscle is another structure which the Herwigs first brought into prominence 

 as an aid in the classification of Actinian polyps. It occurs toward the apex of the column wall 

 in nearly all anemones, and. next to the arrangement of the mesenteries and tentacles, occupies an 

 important place in all Actinological studies. Various type of sphincter are recognized, such as 



i For later results, aee foot-note, p. 541. 



