﻿8 ■ MADEEPORAEIA. 



ring of younger polyps. Most of these are developing close against the turned-up epitheca, 

 which even seems here and there to form part of their walls. They appear also to slope out a 

 little. The ccenenchyma, which appears to be composed of an irregular mass of jagged flakes 

 tilted in all directions, but tending to lie horizontally, is densest in the centre of the saucer, 

 while round the edges it forms a light reticulum. Beyond this reticulum, the elements of 

 which tend to form the jagged plates just mentioned, no definite structure of the crenenchyma 

 can be made out at this stage. The edges of these horizontal plates are quite irregular, being 

 generally deeply incised. The margin of each calicle is formed by one or more of these plates. 

 The septa are not continuous ridges but vertical rows of spines from the edges of these hori- 

 zontal plates. The new calicles appear to be formed by the grouping of the horizontal plates. 

 This young stock is figured in the Ann. and Mag. N. H., ser. 6, vol. xx. pi. ii. figs. 1 and 2. 



Comparing this young specimen with others both young and old, we may summarise the 

 young stage of Montiporte as follows : — 



A well-developed saucer-like epitheca is filled with a mass of reticulum only slightly 

 raised in the centre, where the calicle of the largest or parent polyp of the colony opens, 

 while younger polyps open all round close to the epitheca. 



The fiu'ther typical development may be described as follows : — 



Tlie ccenenchyma. — The coenenchymatous reticulum grows out radially in all directions, 

 either accompanied by the epitheca or shooting out beyond it. The elements of the reticulum 

 all stream outwards, and are either bandlike or filamentous. In the former case, the bands 

 appear from their vertical position to be the remains of the laminate costse which, we assume, 

 at one time surrounded the calicles. The older portions of the corallum commence to thicken, 

 the tissue for the purpose being supplied by threads of the streaming reticulum just mentioned, 

 which bend sharply upwards and downwards, so that three layers are ultimately distinguish- 

 able : — (1) The middle streaming layer ; (2) the lower layer, in which the threads are bent 

 downwards; (3) the upper layer, in which the threads are bent upwards. The middle 

 streaming layer always forms the growing edges, or, in branching specimens, the tips of the 

 branches, and the calicles ih'st appear in it. 



The lower layer, formed by the threads bent downwards, seldom develops to any 

 thickness. It often becomes very dense, or even, when covered over externally by the 

 epitheca, quite solid. The calicles, bent down with it, often protrude slightly, apparently 

 because the layer is not deep enough for them. 



The uppermost layer is that in which the chief characteristics of the genus appear. 

 Before describing them it is necessary to state that in branching types, the axis of a branch 

 is formed of the middle streaming layer, and the bending outwards of its threads radially in 

 all directions forms a tliickening cortical layer which may be perfectly symmetrical and not 

 distinguishable into an upper and a lower. This cortical layer shows all the typical variations 

 seen in the uppermost layer of explanate and massive forms. ■ 



We may enumerate the following specialisations of this important thickening layer : — 



(l) Glalrous. The threads bent upwards grow .without any change in their simple 



