2 MADREPORARIA. 
ment, and, with its allies the Madreporide, seems to stand now at the head of the system in 
the intricacy of its skeleton. 
This intricacy has been such that it has hitherto puzzled all students of coral morphology. 
Milne-Edwards and Haime published a set of beautiful drawings * which they called “the 
structure of Porites,” but they could give us no insight into what they drew. Miss Ogilvie T 
also attempted to elucidate the skeleton by means of ground plans, but her analysis rested 
upon too narrow a basis of comparison. Hence it follows that systematic workers who have 
hitherto tried to describe specimens, being without any insight into the probable or possible 
variations, have had to be content with the most superficial comparisons with previously 
described forms; and the difficulty of this lay in the fact that, though when closely examined, 
the specimens are all different, yet the nature of the differences it has been impossible to grasp. 
Hence the endless repetitions of a certain set of the earliest names. 
Previous to the present writer, no workers, except, perhaps, Milne-Edwards and Haime, 
have had to study the genus comprehensively, and to establish by extensive comparisons of the 
related genera, and of great numbers of forms within the genus, what are the essential principles 
of its structure. Such a study is necessary before any insight can be gained into the variations. 
It was imposed upon the present writer when he undertook to continue this series of volumes 
dealing with the Stony Corals. 
In spite of the fact that the work in the earlier volumes, especially in Vol. IV., had 
already afforded considerable insight into the fundamental plan of structure of the Poritide, 
the difficulties presented by the skeleton in Porites, with its minute calicles, were most 
discouraging. So great, indeed, is its apparent complexity, showing so many subtle differences 
which baftle all attempts to define or even to describe, that the student stands long before the 
task in despair. A beginning of some kind had to be made and attempts at description 
prepared, though with hardly any insight into the inter-relationships of the parts. Slowly this 
uphill work revealed certain constant features. From this vantage ground the descriptions 
were all re-written, when again new points came to light, and so on: each time of re-writing 
fresh principles of structure were discovered, and finally the descriptions had all to be done 
over again. The systematic portion of this volume has been written out in extenso at least 
four times, with the result that the intricate skeleton of this genus can now be reduced to 
order, and the principles of structure minutely described, although we are still far from having 
unravelled the exact nature of many of the variations. 
As one illustration of this gradual dawning of the facts, let me cite the case of the pali. 
These are the most conspicuous elements in the calicle; they have been recognised by every 
worker since the middle of the last century: yet it was only after the present writer had 
written out his first draft descriptions of the whole of the Museum collection that they were 
found to be arranged upon a definite plan. And now, again, it is only as this volume is 
going to press, and when too late to alter the descriptions, that some of the relations of these 
* Ann. Sei. Nat., xvi. (1851) pl. i. { Phil. Trans., clxxxvii. p. 219. 
