470 Mr Gardiner, Notes on Variation, 



Group these two species were found on practically every seaward 

 reef examined by Mr Forster Cooper or myself. A more striking 

 case was that of Madrepora hispida (sp. ?) at Minikoi. It was 

 the commonest coral on the sand flats within the reef of this 

 atoll, to the south and south-west existing as great groves, formed 

 by branches from many colonies. To the north and north-west 

 the same coral was extremely common. The colonies were larger, 

 but only patches on their surfaces or the mere tips of their 

 branches were covered with living polyps. 



It is useless to quote further instances. In my notes a large 

 number of cases of death in corals are recorded, but I did not 

 at the time appreciate the importance nor meaning of the pheno- 

 menon. It is in most instances doubtful as to the extent of 

 the area over which death had taken sway, and I am, except 

 in the above instances, uncertain whether the largest and the 

 smallest colonies of the affected species died. My impression 

 distinctly is that practically all colonies of a species in any one 

 area died, or that there were only the isolated deaths of individual 

 large colonies. 



Each coral block has presumably originated from a single 

 ovum, and such a colony cannot normally give rise to other 

 masses asexually. The limitations in the size of colonies — 

 clearly visible on any reef in massive Porites and other massive 

 genera — points clearly to some prohibition of their growth. Such 

 a regular restriction must be due to some innate reason in the 

 organisms themselves. There can be no rejuvenescence, and the 

 operative cause is, probably, the same as that which ultimately 

 produces the death of our forest trees. The maximum of pro- 

 ductiveness, so far as the formation of the germs of a fresh 

 generation is concerned, is reached, and then the parent gradually 

 becomes less fruitful and ultimately dies. In the animal kingdom 

 there is no close parallel, although it is a reasonable deduction 

 that senile decay occurs in all multicellular organisms or else 

 absolute extinction at some period or other. The phenomenon 

 in domestic animals, a few fish (trout, etc.) and other vertebrates is 

 known, but for comparison with these the whole colony of polyps 

 must be regarded as a single organism. 



If — as I am impelled to believe — the ripening of the genera- 

 tive organs of a large number of polyp colonies . of the same 

 species in a single locality or habitat, followed by the subsequent 

 death of all these colonies, is a regular phenomenon, the con- 

 sequences may be of the most wide-reaching importance in the 

 formation of coral reefs. With this question I am not in this 

 paper concerned. The evidence of it is at present meagre, and 

 the case of Flabellum, where death appeared to depend on size 

 or age, does not lend support to its wide-spread prevalence. 



