PORITES. 7 
round the bases of stems reticular walls frequently appear. It is not always easy to make out 
what method of thickening has produced the effect. Round the bases of thickening stems, 
where no new buds are being formed, one would expect the presence of intervening tissue. 
é The real structure of the wall can, however, as a rule be made out with comparative ease 
when the texture of a reticulum retains its simple rectangular trabecular structure. But the 
problem is rendered very difficult by the tendency of this texture to change into an irregular 
reticulum: even then one can generally recognise the trimurate condition however fluent the 
wall network may be, for the vertical wall pores which correspond with, and indeed are 
parts of the interseptal loculi, can generally be made out. 
Thickenings of the wall by intervening tissue may appear in endless variety. The most 
interesting is that already mentioned (see above, p. 14 and fig. 2, C). A not uncommon case of 
this is where from such a median ridge of intervening tissue the depression of the calicle slopes 
straight inwards, funnel-shaped, the septa appearing wedge-shaped, diminishing inwards to fine 
points and without pali (cf. Pl. IX. fig. 4). 
A second interesting specialisation of the wall is due to the septa being rather more 
lamellate than usual, with a rather slighter development of wall synapticule. In this case we 
find the top edges of the septa appearing as strie across the wall. This is not common. 
Pl. VII. fig. 3 shows a patch in which the walls have become altered so as to take on this 
character. Fig. 5, on the same Plate, also shows the same tendency, though not so pronounced. 
Profound alterations occur in the character of the whole theca, and, indeed, of the whole 
skeleton and of the surfaces of the stock, when the relative proportions of the structural 
elements are altered. The following are some of the more important variations :— 
1. The loss of the rigid rectangular arrangement of trabecule and horizontal junctions. 
This results in various degrees of “ fluency.” 
2. The development of trabeculze as rods at the expense of the horizontal elements, which 
seem to reach an extreme in the specimen shown in Pl. XIV. fig. 5. 
3. The development of the trabecule as lamellie at the expense of the horizontal 
elements. The most striking example of this is seen in the axes of branching or of columnar 
forms. In these the central parts rise as a sheat of lamelle, which bend outwards all round as 
rod-like trabecule. The calicles, opening at the tip, show plainly the lamellate texture of their 
skeletal elements (cf. for instance, figs. 5a and 5) in Pl. XXVIII.; the former showing a more 
lamellate, the latter a more trabecular character of skeleton), 
4, The development of the horizontal elements as lamelle or flakes, with varying degrees 
of degeneration of the trabecule. The extreme of this is met with in P. China Sea 4, in which 
no continuous trabeculae seem to be developed at all, and the skeleton hangs together by the 
irregular fusions of the wavy flakes with short trabecular rods (Pl. XXVI. fig. 2). Many 
branching forms develop thick, flaky, horizontal elements. (See Pl. I. fig. 8, and Pl. XXV. 
fig. 5.) Other specialisations might be mentioned. The elements may seem to be drawn out 
into long thin filaments, or, on the contrary, may be very thick and short ; or one may be thin 
and the other thick. (Cf. for instance, Pl. VIII. fig. 3, Pl. XIV. fig. 7.) While in Pl. II. fig. 1 
D 
