sist the enormous pressure to which they must
be there subjected, amounting, not infrequently, to several tons to the
square inch. And still another point of interest for us springs
from this. It is an inquiry of practical importance to the aquarian
naturalist, How far the diminished pressure which they meet with in the
tank, on being transferred from their lower homes to the aquarium, may
influence their viability. May not some of the numerous deaths in the
marine tank be reasonably attributed to this lack of pressure?

What a difference, too, has Nature established, in the natural power to
resist pressure, between those creatures which float near the surface
and those which haunt the deeper sea! The Jelly-fish can live only near
the top of the water, and, floating softly through a gentle medium, is
yet crushed by a touch; while the Coral-builder bears the superincumbent
weight of worlds on his vaulted cell with perfect impunity.

Another important question is, How far alteration in the amount of light
may affect the more delicate creatures. What fishes do without light has
been solved by the darkness of the Mammoth Cave, the tenants of whose
black pools are eyeless, evidently because there is nothing to see. The
more deeply located Infusoria and Mollusks must dwell in an endless
twilight; for Humboldt has found, by experiment, that at a depth one
hundred and ninety-two feet from the surface the amount of sunlight
which can penetrate is equal only to one-half of the light of an
ordinary candle one foot distant.

Thus ever in gloom, yet in a state of constant safety from storms and
the agitations of the upper air, the thousand forms of low organic life
and cryptogamic vegetation live and thrive in peace and quietness.

"The floor is of sand like the mountain drift,
And the pearl-shells spangle the flinty snow;
From the coral rocks the sea-plants lift
Their boughs, where the tides and billows flow.

* * * * *

"And life in rare and beautiful forms
Is sporting amid those bowers of stone,
And is safe, when the wrathful spirit of storms
Has made the top of the waves his own."[C]

[Footnote C: Percival.]

Upon the bottom, at various depths, lies that brilliant Radiate--type of
his class--the Star-fish. These are quiet and harmless creatures, and
favorites in the aquarium, from the pretty contrast they make with
marine plants and other objects.

The perfect transpar