graceful flight of the sea-turtle under the water,—­the leaping and swimming of the frog,—­the swift run of the lizard, like a flash of green or red light in the sunshine,—­the lateral undulation of the serpent,—­the dart of the pickerel,—­the leap of the trout,—­the rush of the hawk-moth through the air,—­the fluttering flight of the butterfly,—­the quivering poise of the humming-bird,—­the arrow-like shooting of the squid through the water,—­the slow crawling of the snail on the land,—­the sideway movement of the sand-crab,—­the backward walk of the crawfish,—­the almost imperceptible gliding of the sea-anemone over the rock,—­the graceful, rapid motion of the Pleurobrachia, with its endless change of curve and spiral.  In short, every family of animals has its characteristic action and its peculiar voice; and yet so little is this endless variety of rhythm and cadence both of motion and sound in the organic world understood, that we lack words to express one-half its richness and beauty.

FORMATION OF CORAL REEFS

From ‘Methods of Study in Natural History’

For a long time it was supposed that the reef-builders inhabited very deep waters; for they were sometimes brought up upon sounding-lines from a depth of many hundreds or even thousands of feet, and it was taken for granted that they must have had their home where they were found:  but the facts recently ascertained respecting the subsidence of ocean-bottoms have shown that the foundation of a coral-wall may have sunk far below the place where it was laid.  And it is now proved, beyond a doubt, that no reef-building coral can thrive at a depth of more than fifteen fathoms, though corals of other kinds occur far lower, and that the dead reef-corals, sometimes brought to the surface from much greater depths, are only broken fragments of some reef that has subsided with the bottom on which it was growing.  But though fifteen fathoms is the maximum depth at which any reef-builder can prosper, there are many which will not sustain even that degree of pressure; and this fact has, as we shall see, an important influence on the structure of the reef.

Imagine now a sloping shore on some tropical coast descending gradually below the surface of the sea.  Upon that slope, at a depth of from ten to twelve or fifteen fathoms, and two or three or more miles from the mainland, according to the shelving of the shore, we will suppose that one of those little coral animals, to whom a home in such deep waters is congenial, has established itself.  How it happens that such a being, which we know is immovably attached to the ground, and forms the foundation of a solid wall, was ever able to swim freely about in the water till it found a suitable resting-place, I shall explain hereafter, when I say something of the mode of reproduction of these animals.  Accept, for the moment, my unsustained assertion, and plant our little coral on this sloping shore, some twelve or fifteen fathoms below the surface of the sea.