1903-4,] On Aged Specimens of Sagartia troglodytes, etc. 307 
explanation which is complete or quite satisfactory (hut see his 
paper, 1902, pp. 470, 471). 
We are grateful to Mr Gardiner for permission to bring forward 
here some of his observations, not yet published, on the probable 
age of certain large colonies of Maldivan corals * which seemed to 
be dying. His method of estimating the age of these colonies is 
as follows : — The number of polyps on colonies, the age. of which 
is approximately known,! is first determined. Each of these 
colonies presumably originated from a single primary polyp, and 
the numerous polyps have been produced by successive budding. 
The number of polyps so produced would increase in approximately 
geometrical progression. Knowing the period required for the 
production of the known number of polyps on the colony of known 
age, it is possible to make an estimate of the age of the old colonies 
of the same species from the number of polyps of which they are 
composed. Mr Gardiner finds that the results of his examination 
of several colonies are strikingly uniform, giving a maximum age 
of twenty-two to twenty-eight years. 
It is therefore probable that the duration of life in solitary 
corals like Flabellum is about twenty-four years, and in colonial 
corals such as G-oniastrcea, Prionastrcea, Orbicella , and Pocillopora , 
from twenty- two to twenty- eight years. 
LITERATURE. 
1848. Dalyell, Sir John Graham, Rare and Remarkable 
Animals of Scotland, vol. ii. ch. 10, London, 1848. 
1860. Gosse, P. H., A History of the British Sea Anemones and 
Corals , London, 1860. 
1868. Hincks, T., A History of the British Hydroid Zoophytes , 
vol. i., London, 1868. 
* Goniastrcea retiformis, Prionastrcea fuscoviridis, Orbicella laxa, and 
various species or facies of Pocillopora. 
f These colonies must Lave grown up (from ova) within a period “certainly 
less than three years, and probably not more than two years and ten months.” 
They were obtained from a canal cut through the reef of Hulule, which is 
regularly cleaned out once every three years. See J. S. Gardiner, The 
Fauna and Geography of the Maidive and Laccadive Archipelagoes, vol. i. 
pp. 329, 330, Cambridge, 1903. 
