ADULT COLONY. 53 



appears as if the fibers from the synapticulum itself were bracing the two 

 septa. The first are known as false synapticula and the second as true 

 synapticula, but, as all recent writers have pointed out, there is no morpho- 

 logical distinction between the two. Both kinds appear in any section of a 

 corallite. Whether one or the other form is present depends mainly upon the 

 interval between the two septa. Where sufficiently close, as towards the 

 middle of the calice, the interseptal space can be bridged without the forma- 

 tion of a new center of calcification, while such is necessary when the interval 

 is wide, as towards the periphery. 



Miss Ogilvie (1897, p. 168) considers that in Fung ia the. synapticula are 

 formed by special interseptal invaginations of the basal wall of the polyp 

 subsequent to the septal iipgrowths, without ever perforating the mesenteries, 

 and assumes such to be the case with Siderastrea. Bourne (1886, p. 47) has 

 alreadjr shown that in Fungia the mesenteries are really pierced by the 

 synapticula, Fowler (iSSS, p. 8) has accomplished the same for Stephano- 

 phyllia formosissima, and I for Siderastrea siderea (1902, p. 487). The con- 

 ditions revealed by the liberated lamella on plate 6, fig. 33, prove that the 

 synapticula are the products of definite areas of the original skeletogenic layer 

 producing the septa, not of special secondary basal upgrowths. Delage & 

 Herouard (1901) have accepted Miss Ogilvie's interpretation of synapticular 

 formation, giving diagrammatic figures to illustrate how the upgrowth is 

 supposed to take place. 



COLUMELLA. 



The columella is represented in the mature calice by a more or less 

 compact, column-like structure forming the floor of the middle of the calice. 

 In decalcified polyps it is found to have elevated the central part of the 

 skeletogenic tissues in a tubular manner considerably beyond the peripheral 

 parts. Its superficial appearance varies much in different calices ; it may 

 be either papillose or smooth, dependent upon the degree of calcification of 

 the colony. Sometimes only one large, tooth-like papilla occurs, or there 

 may be two close together ; in others, again, there are two or three large or 

 chief tubercles along with several minute projections, or it may be formed 

 wholly of small, scarcely perceptible granules, when, to the naked eye, it 

 appears compact and smooth. This latter condition is found in coralla of 

 which all the parts are strongly calcified. In these the columella is conspic- 

 uous, raised for a short distance above the septa, and its free surface nearly 

 smooth. 



Where several prominent tubercles are present some seem as if con- 

 tinuous with the teeth of the septa, suggesting that the columella is formed 



