Here, then, we have a parasitical insect specialized in the highest degree, yet retaining all its pristine faculties unimpaired, its love of liberty, and of associating in numbers together for sportive exercises, and well able to take care of itself during its free intervals. And probably when thrown on the world, as when nests are blown down, or the birds get killed, or change their quarters, as they often do, it is able to exist for some time without avian blood. Let us then imagine some of these orphaned colonies, unable to find birds, but through a slight change in habits or organization able to exist in the imago state without sucking blood until they laid their eggs; and succeeding generations, still better able to stand the altered conditions of life until they become practically independent (like gnats), multiplying greatly, and disporting themselves in clouds over forests, yet still retaining the old hunger for blood and the power to draw it, and ready at any moment to return to the ancestral habit. It might be said that if such a result were possible it would have occurred, but that we find no insect like the Ornithomyia existing independently. With the bird-fly it has not occurred, as far as we know; but in the past history of some independent parasites it is possible that something similar to the imaginary case I have sketched may have taken place. The bush-tick is a more highly specialized, certainly a more degraded, creature than the bird-fly, and the very fact of its existence seems to show that it is possible for even the lowest of the fallen race of parasites to start afresh in life under new conditions, and to reascend in the scale of being, although still bearing about it the marks of former degeneracy.