ANALYSIS AND DISTRIBUTION OF TYPES OF CALICLES. 273 
hence we ought to find extraordinary variation in this respect. That, however, is not the case, 
The rule is that the composition of the wall is very uniform. We find, for instance, that 
while in valleys and depressions where the calicles are squeezed together the trabecule of the 
calicular skeleton may be almost indefinitely aborted, on convexities where the calicles have 
abundance of room it is seldom that more than one extra trabecula appears. If the convexity 
rises very rapidly the trabecule may all disappear as such, and the skeleton becomes a 
streaming lamellate network. 
Fic. 4.—Diagrams illustrating the structure of the theca of Porites. A, an ideal vertical 
section through a simple walled calicle of a colony ; w, the wall trabecula ; sg, the septal 
granule ; p, the palus; cf, the central tubercle (these three are seen, like w, to be the 
tips of trabecule). B, a horizontal section of a calicle in a colony in which the thece are 
slightly separated so that the synapticule joining the wall trabecule (w!) with those of 
adjacent calicles (w?) have a zigzag course. C, a vertical section through a compound 
wall, which appears when the simple walls (w) are far enough apart to admit of an inter- 
vening trabecula, in this case figured as rising above the walls (w) as a wall-ridge (w7), 
making w look like another granule of the septal edge (the “wall granule”). D, an 
ideal parent calicle to explain the origin of intervening trabecule ; they are homologous 
with costal trabecule (c), one or more of which are able to appear if the calicles in a 
colony are far enough apart to admit them ; ep, epithecal saucer or prototheca. 
We have, then, nothing to do but to go forward and endeavour to arrange those 
phenomena in the Porites calicle which alone seem to admit of tabulation, and those are the 
variable numbers of trabeculee which appear in the composition of the walls, and their leading 
methods of association. The four main divisions are the following : 
A. Those in which a varying number of costal trabeculee always play a conspicuous part 
in wall formation. These are the ccenenchymatous forms of this volume (Synarea of 
Authors). 
bo 
SZ 
