192 Prof. P. M. Duncan on the Hard Structures of 



septa are lamellar, straigjit or wavy, and projecting ; the free 

 edge may be thin and wavy, but in the species under exami- 

 nation it is not ragged, trabeculate, or spinulose. What 

 perforations there are in the septa are small, distant, regularly 

 placed, and are in continuation with the openings between 

 some elongate dentations on the septal edge. Considering 

 what has been written by some paleontologists about per- 

 foration of the septa being a characteristic of the section 

 Perforata, it is necessary to remark that imperforate septa are 

 the rule in all those species of the genus Madrepora that I 

 have examined. 



The Growth of Gemmxde Sclerencliyma, 



The growth of new gemmules takes place from the outside 

 of the axial or apical corallite, from the external surface of 

 the corallites which were buds and liave elongated, but rarely 

 from the surface opposed to the apical corallite, and also, from, 

 the surfaces around the bases of the corallites. In no instance 

 do the gemmules of this species arise from the calicular 

 margin, and their starting-point is remote from it. More- 

 ^)ver, the minuteness and evidently recent development of the 

 9riginating gemmule proves that the calicular margin has not 

 grown in advance since budding commenced, so as to separate 

 the Ipud from the calicular margin. 



Gemmation from a Secondary Corallite. — The first appear- 

 ance of a bud is accompanied by a trabeculate growth from 

 the free edges of two adjacent costaj; the trabeculate growth 

 is thin and arches across the intercostal space, covering it in 

 and closing it, and forming a little hood, looking towards the 

 free end of the corallite. Dentations then arise from the free 

 edges of the costse on either side of the first two, and these. 

 new growths increase in size and join the hood-like structures 

 by bending over and forming a ragged arch. Other cost^e, 

 on either side, are subsequently implicated in this process of 

 hood-making in a similar manner, and a small, perforate, low- 

 arched hood with a ragged open margin covers two or three 

 intercostal spaces, with their original perforate spaces and no 

 others. The costal remain for a greater or less time, and 

 then appear to become absorbed ; or one, the median, may 

 remain and occupy the position of a septum. 



The growth of the bud resembles that of new mural tissue, 

 from the costte and spinules during exogenous growth ; and 

 it is evident that when gemmation occurs from the new mural 

 growth the same simple arching-over of trabeculse into a low 

 hood occurs. But there is this difference : in the case of the. 

 budding from the outside of a corallite which only has a simple 



