can be counted.  As these are all double, this would give five thousand seven hundred and sixty cells to the square inch.  Now a moderate-sized specimen will afford, with all its convolutions, at least one hundred square inches of wall, which would contain a population of five hundred and seventy-six thousand inhabitants,—­a very large city.  So says Mr. Gosse.  We cannot forbear, with him, from quoting Montgomery’s lines on the labors of the coral-worms, which modern science has enabled us to study in our parlors.

“Millions on millions thus, from age to age, With simplest skill, and toil unweariable, No moment and no movement unimproved, Laid line on line, on terrace terrace spread, To swell the heightening, brightening, gradual mound, By marvellous structure climbing towards the day.  Each wrought alone, yet all together wrought, Unconscious, not unworthy instruments, By which a hand invisible was rearing A new creation in the secret deep. .....I saw the living pile ascend, The mausoleum of its architects, Still dying upwards as their labors closed; Slime the material, but the slime was turned To adamant by their petrific touch:  Frail were their frames, ephemeral their lives, Their masonry imperishable.”

The deep-sea soundings taken recently for the Atlantic telegraph have demonstrated the existence of organic life even at the bottom of the ocean.  Numerous living Infusoria have been brought to the light of day, from their hidden recesses, by the lead.  “Deeper than ever plummet sounded” before these latter days, there exist myriads of minute creatures, and of Algae to furnish their food.  It is an unanswered problem, How they can resist 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.