THE GENUS ALVEOPOEA "WITH THE EAVOSITID^. 505 



few of which early stages have beea described. Further, the 

 argument may be advanced that the skeleton formed by the 

 secretions of the smooth outer skin of the original coral polyp 

 preceded the complicated internal skeletons, which may be 

 regarded as having been due to local irregularities in the amount 

 of the secretion pushing in the skin into complicated folds, which 

 folds continued to secrete skeletal matter. Further, it seems 

 to me, that the conclusions arrived at by v. Koch and summed 

 up in his recent paper in Gegenbaur's 'Festschrift,' vol. ii., are 

 essentially in accord. It may, perhaps, be of use topo- 

 graphically to distinguish between basal plate and epitheca ; but 

 we owe so much to v. Koch in unifying our conceptions of the 

 morphology of the Madreporarian skeleton that it seems quite in 

 a line with his own teaching to speak of foot-plate and epitheca 

 as forming together a primitive epithecal cup. I would even go 

 further in the same direction and claim, as above suggested, not 

 only that an epithecal cup was the primitive coral-wall, but that 

 the whole of the septal skeleton built upon it was due to 

 infoldings of the same secreting surface. From this point of 

 view, the whole of the internal septal skeleton may be regarded 

 as an infolding of the epitheca, the median black line showing 

 where the skeletal surfaces are apposed. In this way I think 

 the skeleton of Flalellum, as revealed in sections *, receives its 

 simplest interpretation. I am therefore quite in accord with 

 V. Koch in regarding the external wall of Flahelliom as a 

 secondarily thickened epitheca. 1 may add that this secondary 

 thickening of the epitheca is quite a common feature in the 

 genus Montipora. 



The skeleton of the parent polyp of an Alveoporan colony is 

 in the stage illustrated by the diagram (fig. 6), in which the 

 primitive deep epithecal cup has become provided with septal 

 spines, which were not primitive. 



II. (Figs. 7, 8, 9.) The septa, which early became laminate, 

 owing perhaps to an ever increasing depos^ition of skeletal matter 

 between the mesenteries, formed in time a ring of tall, radially 

 arranged plates, which rose high above the rim of the epi- 

 thecal cup; this latter, in many cases, widening out considerably 

 as a saucer-shaped basal plate. This ring of radial exsert laminae 



* Cf. the figures given by Dr. Fowler and Mr. Bourne in their articles in the 

 Q. J. M. S. xxviii. 18S8, and by t. Koch in Gregenbaur's ' Festschrift,'^ vol. ii. 

 Ortmann's figure, which differs from these, will be discussed further on. 



