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. 
