Although we do not see these infinitesimal creatures at work, their proceedings are none the less real; and though their operations are infinitesimal, the aggregate results are vast and in the highest degree important. It may be shown—1. That, as food, they feed a greater number of beings than any other kind of organisms; 2. That, as scavengers, they eat more refuse than any other group of organisms; 3. That, despite their minuteness, their fossil remains are much greater in bulk and of far more consequence than those of large quadrupeds and serpent-like monsters, such as the mastodon, megatherium, plesiosaurus, ichthyosaurus, etc.; 4. That, as builders, they have produced immense structures, which far surpass in size all the colossal works of man. The evidence of these statements will be presently given; but meantime it may be remarked that such grand results redeem the study of microscopical objects from that pettiness which is often imputed to it.
But not alone because of their stupendous effects are these invisible creatures entitled to our attention. It is in the simplest and smallest creatures that we find the alphabet of the science of life. The rudimentary objects of biology are invisible; and the language of the science could never have been acquired except by first learning its A, B, C with the microscope. It is by the study of the lowest elementary forms of life that we become enabled to comprehend its higher and more complex forms, and we never could have done it otherwise. The anatomy and physiology of our own bodily structures have their roots in the invisible. The grand chain-work of relations that binds all things in order thus loses itself at one extreme in the infinitely great, and at the other in the infinitely small. Embryology, the playground of evolution, shows us microscopic embryos like adult micro-forms as necessary links in the unity of natural phenomena, so that the relationship of living things can only be comprehended by a study of the minutest objects. I do not, however, propose here to enlarge upon this aspect of the subject, but simply to offer a few illustrations of the importance of these micro-organisms.
Let us first consider the relations of microscopic animals to the crust of the earth, and notice what they have had to do with its formation and constitution. From their low grade of organization they are naturally supposed to have been the earliest creatures on our globe, and there is evidence in favor of this. In ancient geological ages, in whose rocks they are scarce, or hardly to be found at all as fossils, there lived numerous worms, mollusks, etc., which could not have subsisted without them as food. We may conclude, with some degree of certainty, that they were almost as plentiful then as now, probably more so; but we could not expect these delicate and minute objects to remain preserved until the present, to have withstood the metamorphoses of the very rocks in which they were imbedded. On this account they are exceedingly rare in the oldest formations, while the
