li 



MADREPORARIA. 



But this interdependence is also a cause of much confusion, for one of its consequences is 

 that slight accidental changes in the growth-form are sufficient to change the type of the 

 calicle. This being so it is evident that the foundation which our knowledge affords is too 

 shifting for the establishment of stable groups, and the question even as to the existence of such 

 gi-oups must remain unanswered. Moreover, if they exist, it is hardly to be expected that 150 

 forms alone, collected casually one from this spot and one from that, not only from the whole 

 area, but from all the different strata of that area where and in which the genus is found, 

 could yield us a survey wide enough to enable us to distinguish them. The material is only 

 just sufficient to enable us to answer the morphological inquiries without which useful 

 systematic work is impossible. It is not even sufficient to show us more than small fragments 

 of the range of actual variation. Series, therefore, could Irardly be expected. We have, how- 

 ever, discovered certain types or repetitions of structure which may be profitably arranged into 

 morphological groups, though these groups cannot be called " species." * 



The only specimens showing unmistakable genetic affinities are those which have been 

 gathered from the same spot, and are obviously daughter colonies of one and the same parent.t 

 The largest area over which such a genetic group is as yet known to spread is that of the 

 Maldive Islands. One simple form of Gonioporan colony, with calicles which are those 

 characteristic of its type of growth, J has been discovered by Mr. Gardiner occurring at con- 

 siderable depths round at least four of these islands. The fact, however, that we here have a 

 genetic group seems to me to be of less real importance than the evidence which the specimens 

 themselves yield that they all alike developed on a soft, muddy bottom. This determined the 

 growth-form, and the gi-owth-form is, as we have seen, largely responsible for the type of the 

 caUcles. 



It is impossible, therefore, to argue that because we have a stable genetic group extending 

 over a given area, similar groups can be assumed for every single specimen that comes to 

 hand. The assumption may be true or it may be false. Nothing is gained by assuming either 

 one or the other. We must discover the facts. 



My own opinion, given with diffidence, is that the Stony Corals are still too elementary in 

 their organisation to be able to acquii-e any but transient stability, § if such an expression can 

 be admitted. I am disposed to think that they respond very quickly to the environment. 

 Where cases of two distinct forms of the same genus are found growing side by side, and thus 

 obviously in the same environment, one of them is probably a new arrival ; the differences 

 between them will sooner or later disappear. If it be not so, I do not see how we are to 



* Professor Doderlein, in his monograph of the genus Fuiigia (see footnote p. 191), which con- 

 sists of single calicles not complicated by colony formation, has discovered structural groups which 

 he calls spedes. Had the forms so gi-ouped united into colonies, the variability seen in them would 

 have been immediately intensified and the nehulousness of the groups greatly increased. The 

 strength of Professor Doderlein's groups rests largely upon the fact that he had at his disposal an 

 immense collection of these simple corals, which are easily packed and transported. 



t This Catalogue, Vol. II. p. 30. | Of. G. Maldivei- 4, p. 59. § Cf. 0. Sussex 1, p. 147. 



