At the outset we find a pre-scientific period as to which we know little; for these essays in classification differ, according to times and races. The Bible, Hindu literature, the primitive poets and historians of Greece, do however provide sufficient indications of the manner in which man originally classified other living beings. The repartition was usually made in three great categories, according as the animals lived in the water, or upon the earth, or flew in the air. The subdivisions are remarkable. Thus, among terrestrial animals, there are some that walk, and some that climb: in this last group there is a mixture of articulate creatures, of molluscs, reptiles and amphibians. Among aerial animals, we find birds, and many flying insects. These primitive classifications are based upon perception far more than on abstraction, or at any rate rest upon superficial resemblances. The habitual environment, air, water, earth, determines the cardinal classes. Some easily apprehended characteristic makes the subdivisions: e. g., flight (birds, insects), locomotion (walking, climbing). The method employed is hardly superior to that by which generic images are formed; and in the order of classification, this point corresponds with the concrete-abstract period of primitive languages, numerations, and religions, i. e., to a gross generalisation fixed by a word. The scientific period begins with Aristotle. It has been affirmed that he owes numerous points to predecessors whom he fails to mention: this is a historical matter of no interest in the present connexion. With him, or under his name, we have the commencement of comparative anatomy which involves a preliminary labor of analysis, unknown in the pre-scientific period, and marking the transition from apparent and superficial to profound and essential resemblances. His classification is of course imperfect, often inconsistent; it bears the impress of an epoch of transition. His terminology is poor, unstable, floating. He distinguishes two sorts of groups only: the genus (γένος) and the species (εἶδος). “But the term γένος has the least constant significance: it serves as the indistinct designation of any group of species, however great its extension, as well what we now term classes, as other lower groups.”[78] Sometimes however Aristotle speaks of large genera (γένη μέγαλα) and of very large genera (γένη μέγιστα), without any precise denotation. It has been said that penury of words was an obstacle to him: yet this is hardly a plausible reason, seeing that he found means to create the word ἔντομα to designate insects. The true obstacle was the insufficient determination of character.