134 ME. H. M. BEENAUD ON EECENT POEITID^. 



only increaee by the formation of folds. We can well under- 

 stand how such puckering might be rttdial in tbe bases of the 

 mesenterial chambers, but quite irregular in the base of the 

 central cavity, where the radial puckers would meet and fuse 

 together with twists and curves. Under the radial puckers, the 

 ectoderm would secrete the septa; under the central, the 

 columella. This view finds some support in the fact that fresh 

 septa are added by puckering of the ectoderm just below the rim 

 of the epitheca (or subsequently of the theca) of the growing 

 coral, i. e. just where the polyp is trying to expand*. 



Again, in endeavouring to establish my argument that the 

 septa arose from infoldings of the epitheca, I appealed to sections 

 of Flalellum. While this appeal is, I think, perfectly justifiable, 

 the sections demonstrating in a remarkable way the point it was 

 desired to establish, yet I confess that, at the time, I did not see 

 that this case itself (Flaiellum) required explanation. For such 

 direct infoldings of the epitheca from the external surface cannot 

 be considered as primitive. As far as we can see, the epitheca 

 must primitively have formed a continuous calcareous layer, and, 

 when infoldings began, they must have risen from its inner 

 surface without the possibility of there being any external scar 

 such as necessarily exists in the case of chitinous infoldings in the 

 Arthropods, at least until secondarily obliterated. The direct 

 infoldings of the epitheca of Flabellum with external scars are 

 therefore somewhat startling. Dr. Ortmann's sections of 

 Flabellum, it is true, show an external layer but with a cir- 

 cumferential dark line t, indicating that this layer itself was 

 formed under a fold. I have already suggested thab this discre- 

 pancy between Dr. Ortmann's sections and those of Dr. Powler, 

 Mr. Gr. C. Bourne, and Dr. von Koch can be explained by sup- 

 posing that, in the case of his specimens, there had been a bagging 

 of the soft parts over the rim of the epitheca which would cause 

 it to grow as u fold. That some specimens do thus bag over we 

 know from Moseley's account oi Flabellum {ChaW.^e-p.ii.ip. 162, 

 1881). But this folded rim is not exactly what is wanted. We 

 should have expected a simple rim of epitheca without any dark 



* In my former paper I described other results of this effort to grow, viz. 

 the bagging of the polyp or even its overflowing over the rim of the epi- 

 thecal cup. 



t Zool. Jahrb. iv. (Syst.), pi. xviii. fig. 9 (1889). 



