Again, all the horses and donkeys neigh; for the bray of a donkey is only a harsher neigh, pitched on a different key, it is true, but a sound of the same character—­as the donkey himself is but a clumsy and dwarfish horse.  All the cows low, from the buffalo roaming the prairie, the musk-ox of the Arctic ice-fields, or the yak of Asia, to the cattle feeding in our pastures.

Among the birds, this similarity of voice in families is still more marked.  We need only recall the harsh and noisy parrots, so similar in their peculiar utterance.  Or, take as an example the web-footed family:  Do not all the geese and the innumerable host of ducks quack?  Does not every member of the crow family caw, whether it be the jackdaw, the jay, or the magpie, the rook in some green rookery of the Old World, or the crow of our woods, with its long, melancholy caw that seems to make the silence and solitude deeper?  Compare all the sweet warblers of the songster family—­the nightingales, the thrushes, the mocking-birds, the robins; they differ in the greater or less perfection of their note, but the same kind of voice runs through the whole group.

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 zooelogical 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