13*3 THE VOYAGE OF H.M.S. CHALLENGER. 



or the tertiary (PI. I. fig. 5 a). In some specimens there are fourteen major septa and 

 chambers only, and fourteen pali. In the only very large specimen obtained (PI. I. 

 fig. 4 «), which is somewhat broken, there appear to have been twenty-four pali, with a 

 corresponding development of the septa, which however are a little irregular. In one 

 young specimen, measuring 12 mm. in height, and 10 mm. in longer diameter of the 

 calicle, there are twelve pali, and the major chambers show evidence of having been 

 twelve originally, but two of them contiguous to one another at one end of the long 

 axis of the calicle have developed additional septa so as to appear as four major 

 chambers ; in these, however, pali are wanting opposite the so-called tertiary septa. Two 

 of their septa which have taken upon themselves, by the subdivision, the rank of primary 

 or secondary septa, have nevertheless opposite them still each a palus. As the coral 

 widens in growth, and these new septa of first order assume their full dimensions, no 

 doubt their pali become lost to view, and partly fused with the columella mass, partly 

 incorporated in the growing septa. Two new pali must be developed in front of the 

 two new tertiary septa to make up the fourteen, and in the young specimen now under 

 consideration a trace of one such new palus has commenced to grow in front of one of 

 the four septa. The accompanying diagram will explain the mode of multiplication of 

 the chambers and septa. The major septa are marked a, those of secondary size or the 

 tertiary b, the new major and tertiary septa a and b' respectively, the pali jj>, and the 



a 



Diagram showing the mode of development of new septa and pali in Caryophyllia communis. 



new palus p" . The new chambers develop in this coral in the same manner therefore 

 as in Flabdlum irregulare as described by Semper, 1 that is to say, the additions to the 

 septa take place in the chambers at the ends of the longer axis of the calicle. It would 

 seem probable that in some instances a pair of extra-major chambers develop, as in the 

 young specimen first described, only at one end of the oval calicle ; hence are derived 

 the specimens with fourteen pali. In other instances, probably, a pair of additional 



1 C. Semper, Ueber Generationsweehsel bei Stemkorallen und iiber das M. Edwards' sche Wachsthumsgesetz der 

 Polypen. Zeitsch. fur Wiss. Zool., Ed. xxii., 1872, s. 243. 



