These affinities of the vocal systems among the animals form a subject well worthy of the deepest study, not only as another character by which to classify the animal kingdom correctly, but as bearing indirectly also on the question of the origin of animals. Can we suppose that characteristics like these have been communicated from one animal to another? When we find that all the members of one zoölogical family, however widely scattered over the surface of the earth, inhabiting different continents and even different hemispheres, speak with one voice, must we not believe that they have originated in the places where they now occur, with all their distinctive peculiarities? Who taught the American thrush to sing like his European relative? He surely did not learn it from his cousin over the waters. Those who would have us believe that all animals originated from common centres and single pairs, and have been thence distributed over the world, will find it difficult to explain the tenacity of such characters, and their recurrence and repetition under circumstances that seem to preclude the possibility of any communication, on any other supposition than that of their creation in the different regions where they are now found. We have much yet to learn, from investigations of this kind, with reference not only to families among animals, but to nationalities among men also.... The similarity of motion in families is another subject well worth the consideration of the naturalist: the soaring of the birds of prey,--the heavy flapping of the wings in the gallinaceous birds,--the floating of the swallows, with their short cuts and angular turns,--the hopping of the sparrows,--the deliberate walk of the hens and the strut of the cocks,--the waddle of the ducks and geese,--the slow, heavy creeping of the land-turtle,--the 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'