534 MEMOIRS OF THE NATIONAL ACADE:\IY OF SCIENCES. 



cycle of twelve. Later, .situated l)etween the cxoccelic c_ycle and the primaiy entotentacles, the 

 inembei-H of the second cycle of entotentacles ])egin to appear, as outgrowths from the entocoeles 

 of the second cycle of nie.senteries. 



Thus the exotentacles, whether belonging to the primary or secondar}- order, appeared 

 before the entotentacles, and from the beginning the}' constituted the outer cycle, at first with 

 six and later with twelve members. 



Mesenteries. — For about four weeks no increase beyond tlie six primary pairs of mesenteries 

 toolv place, and the fifth and sixth pairs remained free from the stomodanmi. Then a pair of 

 mesenteries appeared within the dorsal exocoele on each side of the polyp. Their first indication 

 was as two narrow lines along the column wall toward its aboral termination. These were 

 followed by a pair in the right and left middle exocoeles, and later by a pair in each ventral 

 exocoele. For several weeks the pairs remained of ditt'erent magnitudes, corresponding with the 

 order of their appearance from the dorsal to the ventral aspect (fig. 6, p. 456). After the third 

 month they began to extend across the disk, but, like the fifth and sixth pairs of protocuemes, 

 never reached the stomoda-um. 



Caralliiiii. — Three or four days after fixation, the skeleton was first observed in the form of 

 six radiating septal upgrowths, practically equal in size, and situated within the six primary 

 entocoeles, about midway between the outer boundary and middle of the polyp. At the same 

 time a narrow peripheral calcareous ring was formed, its outer surface uncovered by polypal 

 tissues, and undoubtedly to be regarded as the epitheca. Macerations made later show the ring- 

 to be continuous with the Ixtmil jilate, which very early made its appearance. A day or two after 

 the formation of the first cycle of entosepta, the six exocrelic members began to appear, in some 

 cases simultaneously, but in others in successive bilateral pairs from the dorsal to the ventral 

 aspects (fig. 12, p. 4!t2). 



During the course of the third week other calcareous deposits took place, some appearing 

 as augulated continuations of the primary septa, and others arising wholly independent. For 

 two or three months the further development consisted mainly in the increase in size and com- 

 plexity of the parts mentioned, the general impression being that of two cycles of septa, a larger 

 and a smaller, having their peripheral extremity enlarged in a Y-shaped manner, but free from 

 the epitheca. The columella was formed partly from independent upgrowths from the basal 

 plate, and partly by centripetal extensions of the entosepta. 



On the establishment of the second cycle of mesenteries, which naturally corresponded in 

 position with the primary exosepta, new calcareous formations appeared independently at the 

 periphery of the entocfcles, and later fused with the primary exosepta already in the same 

 radius. The peripheral angulations of the primary exosepta became new and independent 

 exosepta, situated within the twelve exocoeles. The skeletal changes now going on were some- 

 what obscure and complicated, l)ut according to my interpretation they aflord clear evidence 

 that the members of the second cycle of entosepta nuist l)C regarded as new formations, even 

 though later they fuse with the remnants of the primary exosepta. The continuations of the 

 primary exosepta remain exosepta. and for the time being constituted the third cycle of septa. 

 A distinct dorso-veatralitj' was manifest in the development of the septa. 



