CORALLUM OF TURBINARIA. 365 
We thus see that many of those features which have been 
relied upon for the discrimination of “species” in this group 
are in reality but of secondary value ; that,as with other corals, 
the characters of a Turbinaria, and more particularly the general 
form of the colony, are largely influenced by the conditions of 
its environment. On the other hand, al/ variation among 
binarians (and the same is equally true of other genera) is 
certainly not the mere expression of adaptive modification. 
This is proved by the fact that specimens living side by side, and 
consequently under exactly the same conditions, so frequently 
exhibit quite obvious differences of types such variation can only 
be genetic. I have myself observed, growing upon the same 
pearl-shell, three large Turbinarian cups which were quite typical 
examples of what must, in my opinion, be regarded as three 
distinct and well-marked species. 
The question of defining the limits of a “species” is in no 
eroup such an easy one as it appears to the student who works 
only at the inadequate material represented in our museums* ; 
and, in the case of the corals, it is a problem of the greatest 
difficulty. At every turn the zoologist who studies Nature, not 
merely in the museum or laboratory, but also in the field, is 
confronted by facts such as those to which I have alluded,—facts 
which bring him once more face to face with that ever-recurring 
question, “ What is a species ?”—a question to which no satis- 
factory answer is as yet forthcoming ; to which, indeed, no satis- 
factory answer can be looked for until such time as taxonomic 
research is placed upon a more truly scientific basis—until, in 
short, the zoological student has at his disposal large series of 
specimens and other data which have been collected with the 
express view of aiding the solution of those problems which are 
summed up in that familiar word “ species.” 
* See a recent note in ‘ Nature’ (vol. lxiii. pp. 490-1), in which the scientific 
collecting of zoological material is discussed. 
