390 
ZOOLOGY: A. G. MAYOR 
The densities also of solid and liquid gallium were determined, — data 
which have especial interest because the expansion of gallium on freezing has 
been attributed by some investigators to impurity. In the first place careful 
determinations were made by means of a pycnometer for solids 3 of the den- 
sity of the impure material containing some indium in the solid and liquid 
condition, the values found being respectively 5.975 and 6.166. Subse- 
quently when the purest material had been obtained, the determinations were 
repeated with equal care, giving values 5.885 and 6.081 respectively. Evi- 
dently indium had produced no essential effect upon the expansion on freez- 
ing and even if the more carefully prepared gallium was not absolutely pure, 
it is evident from the outcome, by extrapolation, that the purest gallium must 
still possess this unusual property. 
1 This method also has since been published by Dennis and Bridgman in their interesting 
article on Gallium. 
2 Richards and Speyers, /. Amer. Chem. Soc, Easton, Pa., 36, 1914, (491). 
s Richards and Wadsworth, Ibid., 38, 1916, (222). 
THE GROWTH-RATE OF SAMOAN CORAL REEFS 
By Alfred G. Mayor 
Department of Marine Biology, Carnegie Institution of Washington 
Communicated October 30, 1918 
In April, 1917, reef corals from Pago Pago Harbor, American Samoa, were 
measured, photographed, weighed, marked by numbered brass tags and 
replaced in favorable situations upon the reef-flats either by tying them with 
wire to iron stakes or imbedding their bases in concrete. 
In July, 1918, these corals were again studied in order to ascertain their 
growth-rate, and as the specimens selected were of average size it was hoped 
that an approximate determination of the average growth-rate for each species 
might be determined. It was our object to calculate the weight of stony 
matter which coral heads of average size add to the reef per annum. In order 
to do this, the weight of the living coral was ascertained both in 1917 and 
in 1918. Then, in 1918, the coral was killed and its animal substance dis- 
solved in KOH, after which the fresh water was largely abstracted by wash- 
ing the skeleton in 90% ethyl alcohol; and finally the coral was dried in the 
sun, and then weighed. 
This showed that the weight of the dried stony substance in various species 
of reef corals is on an average about 0.8 that of the same coral heads when 
alive. Various Acropora ranged from 0.7 to 0.9, while branched Pontes were 
about 0.8, and large massive Porites slightly above 0.9. 
Applying this correction, we find that on these Samoan reefs the gain in 
