MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 491 



on those of CaryophyUin atid other t'orui.s. The corals Lcptopsaiuniui and Cladfrpmmnua^ hi 

 addition to AstroidcK and BdlanopIiyUia, were found with twelve primary .septa appearing 

 simultaneously. 



Prof. G. von Koch's paper (1897), on the development of Can/ophyUia cyat/n/.^, indicates 

 that in this imperforate coral the six entocoelic septa are the first to appear, and ai-e early 

 attached to the theca, which arises a little later and independently of the septa. The alternating 

 exocoelic septa appear somewhat later than the entocoelic, and like them are uniform in size, but 

 shorter in their' radial extent. The basal plate preceded the development of the septa, appearing 

 at first as six independent, somewhat triangular, calcai-eous deposits, which afterwards fused 

 with one another. Here, again, the protocnemes alone are developed, and only as far as the 

 £^dicanhi/i -stage, the fifth and six pairs being incomplete. 



Mj' results on the origin of the septa in the fissiparous coral Manicina areohda, so far as 

 they go, coincide with those of Lacaze-Duthiers and von Koch. The septa appeared as 

 upgrowths of the basal plate, covered on both sides by the basal wall of the polj'p (fig. 137). The 

 first six septa appeared simultaneously, within the entocceles of the larva at the Edwards ia-stii,gQ 

 of mesenterial development (fig. 13.5); on the other hand, no exoctelic septa had arisen when the 

 young polyi>s were preserved, although an interval of over a week had elapsed since the appear- 

 ance of the entocoelic membei"s. There is good reason to suppose, however, that the primary 

 exocfelic members never appear in Manicina, as exocoelic septa seem to be absent from the 

 adult. 



In numerous polyps of Siderastrsea I'odians reared from larxa;, the six members of the 

 primary cycle of septa appeared sinndtaneously, within the six primary entocceles. three or four 

 days after fixation of the larva, and in practically all cases were equal in size. Eai'h septum 

 was at first a simple lamella, with the upper edge distinctly serrated, and the lower edge flat and 

 adherent to the glass to which the poh'p was afiixed. A da_v or two after the formation of the 

 first cycle of entosepta, the six exosepta began to make their appearance, in some cases practically 

 simultaneouslj% but in others in successive bilateral pairs from the dorsal to the ventral aspect 

 of the polyp (p. 102). Thus in fig. 12(', a septum occurs in each of the two dorsal exocceles, a 

 rudimentary meml)cr in each middle exocoele, while in the ventral chamber no skeletal formation 

 is 3'et apparent. Figs. S, c, although representing different stages, were taken from two different 

 polyps of the same age. 



The young polyps of Siderastrsea in the end presented two complete cycles of protosepta, 

 a primar}' cycle consisting of six equal entosepta, and a secondary C3'cle of six equal exosepta, 

 the latter series having appeared later and remaining a little smaller than the former. The 

 protoseptal stage was completed within the first fortnight after the extrusion of the larv». In 

 the later growth of the septa the peripheral extremities assumed a Y-shape, the additional 

 portions appearing in some instances as distinct formations, and in others as continuations of the 

 primary simple septum. 



The a})ove examples all agree in the fact that the six entocoelic septa arise simultaneously at 

 the developmental stage marked by the presence of six pairs of mesenteries, and with the 

 Edwardsian mesenteries alone complete. Lacaze-Duthiers' figures of Balanophyllia, regia 

 indicate that when the septa appear all the twelve mesenteries are united with the stomodreum, 

 l)ut no microscopic sections were made to confirm this. In Astroides, BalanopihylJia, and others, 

 the exocoelic septa appear along with the entocoelic, but an interval elapses in Cktryophyllia, 

 Flahellum, and Sider'astrsea before this takes place, while in J/anicina they are wholly wanting. 

 Where exosepta are developed, the six members usually appear together, hut in certain 

 polyps of S. radians a decided dorso-ventral succession in bilateral pairs was followed. 



The siuudtaneous appearance of the cycle or cycles of protosepta in corals, and their 

 uniformity in size, are in marked contrast with the successive order of development followed 

 by the pairs of protocnemes. In no case do the septsi appear until the six primary pairs of 

 mesenteries ai'e fully established, and then the six members of the cycle arise together. The 

 septal sequence most nearly conforms with that of the tentacular, in which the members of a com- 

 plete cycle, or both inner and outer cycles, appear together. 



