FLORIDA REEFS. 47 
with all these chambers. At the top is an aperture serving as a mouth, 
surrounded by a wreath of hollow tentacles, each one of which connects 
at its base with one of the chambers, so that all parts of the animal 
communicate freely with each other. But though the structure of the 
coral is identical in all its parts with that of the sea-anemone, it never- 
theless i^resents one important difference. The body of the sea-anemone 
is soft, while that of the coral is hard. 
It is well known that all animals and plants have the power of appro- 
priating to themselves and assimilating the materials they need, each 
selecting from the surrounding elements whatever contributes to its well- 
being. Now corals possess, in an extraordinary degree, the power of 
assimilating to themselves the lime contained in the salt water around 
them ; and as soon as our little coral is established on a firm foundation, a 
lime deposit begins to form in all the walls of its body, so that its base, its 
partitions, and its outer wall, which in the sea-anemone remain always 
soft, become perfectly solid in the polyp coral, and form a frame as hard 
as bone. 
It may naturally be asked where the lime comes from in the sea which 
the corals absorb in such quantities. As far as the living corals are 
concerned, the answer is easy, for an immense deal of lime is brought 
down to the ocean by rivers that wear away the lime deposits through 
which they pass. The Mississippi, whose course lies through extensive 
lime i-egions, brings down yearly lime enough to supply all the animals 
living in the Gulf of Mexico. But behind this lies a question not so 
easily settled, as to the origin of the extensive deposits of limestone 
found at the very beginning of life upon earth. This problem brings us 
to the threshold of astronomy, for the base of limestone is metallic in 
character, susceptible, therefore, of fusion, and may have formed a part of 
the materials of our earth, even in an incandescent state, Avhen the worlds 
were forming. But though this investigation as to the origin of lime 
does not belong either to the naturalist or the geologist, its suggestion 
reminds us that the time has come when all the sciences and their 
results are so intimately connected that no one can be carried on inde- 
pendently of the others. Since the study of the rocks has revealed a 
crowded life whose records are hoarded within them, the work of the 
geologist and the naturalist has become one and the same, and, at that 
border-land where the first crust of the earth was condensed out of the 
