4 MADREPORARIA. 



inaamnch as they are assumptions that every specimen which comes into our hands must 

 represent a number of similar forms indefinitely distributed over more or less extensive areas. 

 The only difference between the species and the form is that the former word connotes close 

 genetic affinity of all such similar individuals, while the latter simply says that they resemble 

 one another, their resemblance being either genetic and accidental or convergent. Both these 

 assumptions, although here we are only concerned with the " species," are, as the story will 

 explain, not entirely, but in some important elements, imaginary, and it is just the imaginary 

 elements which have made them as useless for work on the Corals as it will be shown that they 

 have been. 



I repeat that both of these units are imaginary. The " species " is imaginary, inasmuch as, 

 though we are quite justified in postulating a genetic group composed of the closest 

 genetically related forms of every specimen we come across, it fades away in all directions, 

 altering its shape as it goes, and is thus without any definiteness, either of form or distribution. 

 The " form " is imaginary, inasmuch as we do not know of its existence at all. We have far too 

 little insight into the essential form-features of such organisms as Corals to say that any two 

 are alike except most superficially and to the eye of the individual worker, whereas the next 

 student may point out a score of important differences. In order to make any solid progress, 

 we must first of all find a unit of work, the essential of the unit being that it is an ascertain- 

 able and definable fact. 



All who have been following the progress of this Catalogue will have noticed that the 

 futility of the imaginary species was early felt, and was followed by an attempt to discover a 

 new definable unit. A geographical form was suggested as somewhat of a leap in the dark, 

 inasmuch as it was difficult to say what it represented. To all appearance it represented 

 nothing more than the individual specimen, so that classifying by such a unit was apparently 

 nothing more than the description of every individual specimen to begin with, in the hopes 

 that a second step might lead us to some possible grouping in the future. 



The history of the West Indian Porites is, then, especially instructive, as it shows, with 

 singular compactness and lucidity, first of all the disastrous results of working with an 

 imaginary unit, and in the second place that Nature herself offers us an ideal unit, which is 

 not a mere individual, but a local form, that is, a form which seems to be fairly clearly 

 definable for each locality ; indeed, it appears that there may be more than one in any single 

 locality growing side by side without intergrading. This story, then, supplies us at last with 

 a solid content for the geographical name. It is true, of course, that the individual specimen 

 had, strictly speaking, a solid content, but it was meagre in the extreme, and artificial — a pro- 

 duct of the Museum cupboard — whereas the new content is a real fact of Nature taken from 

 her own workshop, and thus supplying us with a small clue to the way in which she works. 

 The discovery of this is the aim not only of all systematic zoology, but of all science. 



I am, of course, aware that, for all we know, these local forms may have hazy and 

 indefinite distributions ; still we now have at least two solid facts of knowledge about them, 

 namely (1) that they have such-and-such characters, and (2) that they are, however indefinitely. 



