MR. H. M. BERNARD ON RECENT PORITIDiE. 



135 



line outside the first begianinga of the septa. The fact that 

 this is not found — cf.^ e. g., Dr. Fowler's sections (Q. J. M. S. 

 xxviii.) — required explanation; and that probably lies in the 

 fact that the puckering of the expanding ectoderm in the early 

 stages of the epithecal cup extends beyond its rim, and that 

 consequently, when this puckered skin secretes its exoskeleton, 

 the latter is puckered or folded from the first. 



The last matter to which I wish to refer is still more important, 

 and, moreover, it brings us back to the main subject of our paper, 

 viz., the afiinities of JPorites. One of the special difiiculties in 

 dealing with the morphology of the Madreporaria lies in the 

 fact that, for precision's sake, we have to idealize the parent 

 polyp and picture to ourselves the possible transformations of its 

 skeleton, as if it remained stationary. But, as a matter of fact, 

 budding and colony-formation come in to complicate matters 

 greatly. This, therefore, we must face as a difliculty in the way 



Fig.]. 



A and B. Epithecate stages; the septa developed ia A, become exsert in B. 

 0. Thecate stage ; the exsert septa replace the epitheca, vrhich becomes 

 vestigial. D. Diagrammatic section of Pontes. 



of our line of argument, "We have, for instance, assumed that 

 the epithecal cup became vestigial because it was rendered 

 unnecessary by the rising up of the septa (fig. 1) above the edge 

 of the epithecal cup to form an internal theca, which supplied in 

 every way a stronger and better-defended retreat for the polyp 

 than the epithecal cup itself with its edges tending to be filmy 

 and friable. Now, while a comparative study of the different 

 forms of calicle leads me to believe that this is actually what took 

 place, yet, when the habit of budding and colony-formation is 

 taken into account, we are forced to ask whether a reason for 

 the degeneration of the epitheca might not also be found some- 



