The next step was the separation of the two great branches of the organic world— plants and animals. The broad features of these groups must have been apparent to primi tive man, but it is only within comparatively recent years that such groups as the sponges, the branching forms of the corals, the spread ing growths of the polyzoans, have been def initely placed among the animals. The names, asea-anemone," °moss-animal,* °zoophyte,' and the like, show the popular error or doubt as to these forms. The relationship of the minute or even microscopic hydroids and pro tozoans were still longer in doubt; and to this day there is a borderland in this great group (the Protozoa) of minute, unicellular objects where no one is able to draw a certain line between what should be called a plant and what an animal, or even whether some of the ob jects are organic at all. • As men perceived certain likenesses and unlikenesses the sorting of plants and animals went on crudely at first, on purely superficial or even fanciful grounds. This sufficed fairly well for some large and well-marked groups, as beasts, birds, fishes, insects, hardwood trees and the like, yet led to many mistakes, such as placing whales with the fish and the bats with birds. Meanwhile students here and there had become interested in special groups, and each called his pursuit a science. Thus arose Orni thology—the study of birds: Conchology, the study of shells (in which for a long time little attention was paid to the animal that made them!) ; Anatomy and Physiology, the study of structure, at first confined wholly to the human form, and only lately to animals in general, when it was distinguished as Compara tive Anatomy; Botany, the study of plants; and so on. In each, men gathered and recorded specimens and facts, as a rule from a single neighborhood. Nevertheless, curiosity began to inquire beneath the surface. Plants were pulled apart, animals dissected and resemblances and contrasts of structure were noted. Naturalists traveled, and found that the creatures of the world were more numerous than had been sus pected, and varied with climate, soil, height above the sea and diverse conditions, and when records and specimens from many localities were gradually accumulated in great museums, like nesses and contrasts appeared that had not been visible in the small local cabinet. Materials were thus obtained for more intelligent ar rangement, and classification became one of the most important sciences in the scope of biology'. The great service an accurate arrange ment of living thin,gs would render to an in (wirer as to their nature was perceived, and scientific men everywhere searched for facts which should fill the gaps in their Icnowledge. The criteria were made more and more exact, and as classification was perfected it became increasingly evident that the. criteria for all branches were substantially similar, and there came to be perceived certain plans of structure. One of the latest and most powerful aids to investigation, the result of the perfecting of the microscope, was the science of Embry ology, or the study of the development of a plant from the seed or of an animal from the egg. It went hand in hand with Histology, the study of tissues, and both disclosed the new truth that the structure of both animals and plants was at its basis the same—a cell filled with °life substance') (protoplasm); and that the multiplication of these cells constituted the growth, and their arrangement and limit the form and bulk, of every animal and plant. It was furthermore ascertained that an egg or a seed (in which it is believed that every animal plant begins, in spite of some apparent excep tions) was simply a cell differing, so far as we can yet see, from other cells in the body only by its possession of the potentiality of inde pendent life under the fostering of suitable conditions. Classification had already shown that its groups might be arranged in some thing like a series from those very simply organized (the one-celled protozoa at the foot of the list) up to the highly complex. Now
embryology showed that the changes each indi vidual passed through from egg to birth were a series of changes from simplicity to com plexity and furthermore that they suggested a parallel to the features of the successive groups in classification, especially to those of the subordinate ranks of the subject's own class. Palmontology enforced this by a similar parallel, finding that the most ancient animals fossil in the rocks were of simple and general ized structure as compared with those of more modern geolog.ical formations; in other words, that structural development has also been his toric development.
All these facts changed the point of view of the biologist. Instead of looking at separate animals and seeking to find differences upon which to make new species and subdivide groups, he is now seeking for likenesses — points of unity. It was long ago suggested to thoughtful minds that the world was not al ways as we found it, but that for a vast period there had been a slow, persistent growth and unfolding: The phenomena of the inorganic world pointed the same way, and hence arose the °nebular hypothesis"— the explanatory theory that the universe developed from a gase ous state, and the earth, as one" of its parts, yvas slowly perfected in pursuance of the forces inherent in its origin. Biologists are only carrying this theory out in a detail when they argue that the facts in their hands can be ac counted for only by the supposition that the living beings on the earth have been slowly developed from a primitive source, comparable to the germ-cell, along unequal and ramifying lines of progress under the influences of their changeable environment. This is only a de tail,— a flower,— of the general unfolding of the universe which is well called its evolution; it is an organic evolution.
In the light of this grand generalization biology is now progressing with an organized force for investig.ation of the great question as to the origin and nature of life. This has not been answered by any of the fruitful hypoth eses, like those of Darwin or Lamarcic, which have placed such effective tools in the biologist's hands. Toward the solution of this problem all scientific men are working, consciously or unconsciously. In aid of this purpose are pushed forward the incessant and world-wide collection and preservation of preserved ani mals and plants—museum specimens; and the systematic and accurate observation arid rec ord of local species and their habits and in stincts. Much of this seems trivial and dry as dust in the eyes of the ignorant or of those minds, being occupied with other thoughts, forget the reason and tendency for these ever-multiplied details of natural history. Patient students toil to the same end in labora tories of anatomy and microscopy, laboriously gather statistics of variation, compile lists of geographical distribution, chisel out of the rodcs remains of extinct races, and sort and re-sort in experimental classifications —all this in order to provide the generalizers of the science with more and better factors for the solution of the great focal problem, What is Life, and how came it to be? What has been the net result so far? In one direction the conviction of the universal eminence and force of the principle of evolution; in another the realization of the independent life and action of each separate cell. To the study of the constitution, qualities and behavior of the cell, whether standing alone in the unfertilized egg, or as a naked monad, or one in an inter dependent association of millions building up a complex org-anism, has biology come at last; and not until it has vanquished the difficulties presented by this atom of living and potential protoplasm, the cell, will it accomplish its full purpose.