MADREPORARIAN CORALS 337 



reproducing or not, though with a long series a size is reached beyond which there is 

 Httle further growth.^ Caryophyllia starts as a polyp of even diameter, developing below 

 it a " basal plate " of corallum on which a cycle of six radiating plates, the primary septa, 

 are deposited. These grow in height, while their sides thicken, along a circle close to their 

 external edges, to produce a ring-like theca, the whole standing up into the base of the 

 polyp. I have found it to be a rule in Caryophyllia — and indeed in most or all coral 

 genera — that, in growth, spaces between septa, if sufficiently wide, are invariably filled by 

 the formation of more septa, which at once connect with the theca, indeed often seeming 

 to be formed on its upper edge. Thus there are progressively added, as the polyp grows, 

 the septa of cycles II (6), III (12), IV (24) and so on. 



Each species of Caryophyllia aims at some definite number of septa and, as the septa 

 at all levels of the skeleton are about equidistant from one another, the corallum has to 

 increase its diameter. This is usually met by the assumption of a horn-like (cornute) 

 shape, but the young polyp may have broadened its basal attachment, so as to allow 

 gaps for septal cycles II and III before upright growth is established.^ In many species 

 this cornute-growth may be masked by the broadening of the whole stem. This is 

 accomplished by the deposition of corallum between and over the outside edges of the 

 septal plates — these are the costae — so as to form a thick wall of solid corallum on the 

 outer side of the circular thecal growth, which is otherwise unaffected; thereby the 

 diameter of the column may be increased several times. For this deposition the polyp 

 tissues outside the corallum are responsible. Such soft parts are easily killed, especially 

 by silt, with the cessation of further skeletal formation, and the naked column then 

 becomes subject to solution and the ravages of boring and other animals. The result may 

 be that a species, which normally grows a broad, straight stem, may become quite 

 cornute, but of course in truly cornute species there is no such thickening. 



Irregularities in growth may take place in all corals and a common development is the 

 assumption of an oval or compressed shape of calice, which in Caryophyllia may be 

 fixed as a specific character. In these species or specimens, as the septa do not become 

 curved in any way, spaces may be left at the ends of the compressed cup. A method 

 here is to form 2 pairs of septa of a new cycle on either side of each terminal or directive 

 septum of cycle I. All the septa here placed then gradually approximate in size to those 

 of existing septa and may be classified into their cycles so that the hexasymmetry is 

 altered ; this is well seen in C clavtis (Scacchi) which usually has 16 systems.^ C. octopali 



1 Cf. Flabellum in "Protandry and Senescence in Corals" {Proc. Camb. Phil. Soc. xi, 463-71, 1902) and 

 Marine Inv. in S. Africa, 11, 115-54, 1902. F. curvatum in the present report lends support to the "size" 

 question. 



^ A growth vertical to the base of attachment is found in the early stages of all corals and is presumably 

 correlated with feeding in the detritus-layer; it is well seen in shallow- water Paracyathus. Disc-like genera 

 later spread horizontally, but the correlation of septal formation to available gaps formed between septa 

 applies to all. 



' The greatest irregularities occur in the details of this growth in corals, whose compression seems to be a 

 matter of environment rather than of descent and is hence not a specific character. Even in the latter two 

 new systems may form first at one end of a calice or even one at each end, an additional two systems appearing 

 more slowly in later grovrth. 



