INFLUENCE OF TEMPERATURE. 97 
highly heated by the sun, is probably one cause leading to the depo- 
pulation of these internal waters. The temperature becomes raised, 
as in a puddle of standing water elsewhere, and is quite unfitted, 
therefore, for species accustomed only to the ordinary tropical tem- 
perature of the ocean. 
Light and pressure and probably the amount of air in sea-water, in- 
fluence the growth of corals, so far as to fix limits to their distribution 
in depth. It is a little remarkable that those families which have a 
wide geographical range, have also a great range in depth: for 
Caryophyllie, Dendrophyllie, Oculine, Gorgonide, and Hydroidea, 
are found even at depths of one or two hundred fathoms; while 
Madrepores and Astras, and all the ordinary reef-forming species, 
scarcely exceed a depth of twenty fathoms. 
Temperature has little or no influence in determining this range, 
although it has been so asserted: 66° is not met with under the 
equator short of 75 or 100 fathoms. ‘The following table gives ap- 
proximate results for the winter months, from observations on this 
point by different navigators in the Pacific. It is well known that 
these averages are much varied in particular regions by currents. 
Latitude. Depth of 66° Fahrenheit. 
N. Latitude. 28°—30° : - = 15—25 fathoms, to surface. 
25° - - - 25—30 Ue 
20° - - - 30—50 ce 
15° - - - 40—60 & 
10° - - - 50—75 ce 
5° - . - 79 -s 
Eavuator. 0° - - : 75—100 “ 
S. Latitude. 5° : E = 50—75 ce 
10° - - - 50 ae 
15° - - - 50 ce 
20° - - - 40 a 
25° - - - 25 aC 
28°—30° °.- - - Surface. 
It appears, therefore, that among the causes limiting the range of 
corals in depth, light and hydraulic pressure must have great in- 
fluence. The proportion of atmospheric air present may be another 
cause. Yet according to Darondeau, the deeper waters contain more 
atmospheric air and also more carbonic acid,—the difference being as 
much as ;1,th the volume of the water.* 
* Examination of Sea Water collected during the Voyage of the Bonite, Jameson’s 
Edinb. Jour., July 1888, p. 164, Darondeau’s observations require confirmation. 
25 
