272 MADREPORARIA. 
Taste IV.—ANALYSIS AND DISTRIBUTION OF THE MORE EASILY 
DEFINABLE TYPES OF CALICLES. 
In the Morphological section of the Introduction (p. 12) there will be found an analysis of 
the fundamental structure of the calicle of Porites. This was essential before we could obtain 
any insight into the real nature of the innumerable variations which the genus presents. 
Each separate variation is due to some special development or abortion of one or more of the 
structural elements. 
In the following analysis we shall have to confine ourselves to the more important of 
these variations, viz., to the structure of the walls. Other variations are here regarded as, 
comparatively speaking, incidental. 
We again start from our ideal parent calicle D, shown in fig. 4, with its rings of 
intra-calicular and extra-calicular or costal trabecule ; regarding the ring marked w as the 
typical wall trabecule, all on the inner side being intra-, and all outside being extra-calicular. 
The following tables will chiefly deal with the various compositions of the dividing walls out 
of these trabecule, treating the latter for practical purposes as morphological units. As this 
seems to be in direct opposition to the principles laid down in 1899* when discussing the 
“trabecula” of Milne-Edwards and Miss Ogilvie, viz. that it is only so much tissue 
intervening between the rows of perforations through the septa, and not the all-important 
morphological unit they assumed it to be, it is well to point out how circumstances may 
temporarily alter cases. One strand of a tissue more or less makes no difference where there 
are many, but if there are one, two or three, then one more or less becomes of immediate 
importance, especially if such variations in amount entail structural variations in other parts 
of the organism. This is the case with the trabecule of Porites, in which genus, owing to the 
small size of the calicles, asingle ring of trabeculee may represent, say, the pali, and thus be of 
morphological importance. But that this does not in reality bestow importance on the 
trabeculee as such we gather from the ease with which even in Porites they may all disappear 
and run together into lamellate plates. 
It is necessary therefore for the student to bear in mind that we are dealing in a tentative 
manner with the phenomena without being at all sure of the morphological importance of the 
factors with which we are dealing. All we can say is that in the vast majority of cases the 
trabeculee seem to fall into the following different arrangements, just as if they were stable 
elements. For example, as already pointed out in the Introduction, the number of the 
trabecule in the walls of a Porites colony should depend upon the width of the ealicles apart ; 
* Journ. Linn. Soc., Zool., xxvii. p. 137. 
