Vol. 69.] THE GENUS AULOPHYLLZ'M. 63 



vesicles. These changes are shown diagrammatically below (fig. 6). 

 They approximately synchronized with* the separation of the septa 

 at their inner ends. The arched tabuhe broke up further to 

 form the ' walls ' of the central column 

 pjcr. fi. (the pericentral vesicles), and with- 



in these was laid the irregular tabular 

 tissue (the central vesicles). Both the 

 central and the pericentral vesicles became 

 more numerous, and produced a denser 

 structure (PI. VI, fig. 4 b & PI. VII, 

 fig. 3 b). 



(e) The dissepiments. — The develop- 

 ment of the dissepiments followed upon 

 the introduction of the minor septa. A 

 single ring of dissepiments first appeared 

 (PI. V, fig. 5 «), but the number increased 

 as the coral grew. The outward expan- 

 sion of the zone was interrupted at short 

 irregular intervals by a wider ring of dissepiments being fol- 

 lowed by a narrower one. Thus sharp ledges check a short, 

 period of gradual expansion, and the result is the wrinkled aspect 

 to which the Pugosa owe their name (fig. 1 a, p. 58). 



The dissepiments are not derived from tabulae, as are the tabular 

 vesicles. They approach more closely the nature of coenenchy- 

 matous tissue. In conjunction with the minor septa, their function 

 may have been the expansion and strengthening of the calicular 

 wall. A layer of dissepiments was deposited against the epitheca 

 inside the rim of the calyx, at the same time as the floor of the 

 calyx was raised by a fresh platform of inner tissue. Hence, at 

 any one level, the outer dissepiments are of earlier growth than 

 the tabular vesicles which abut against them. 



Rate of Growth, and the Size attained. 



The diametric measurements attained by a corallum differ 

 greatly in different individuals, as also does the rate of develop- 

 ment. Some individuals show signs of approaching maturity at 

 the same distance from the proximal end and with the same 

 diameter, at which others have only reached an early stage of 

 development. Consequently, these forms remain dwarfed in size, so 

 far as the diametric measurements are concerned (see PI. V, 

 figs. 8 & 9). 



The comparison of individuals with reference to their height can 

 serve no useful purpose, since it cannot be known to what length 

 a certain coral might have attained had not the death of the polyp 

 terminated its growth. 



