We have thus seen, from a shapeless hole to these complex dwellings, every possible stage; we have found among animals the rudiments of the different human habitations, certain animals, indeed, having arrived at a degree of civilization which man himself in some countries has not yet surpassed, or even indeed yet attained. MAN’S FIRST APPEARANCE --BOYD DAWKINS The characteristics of the evolution of living forms may be summed up as follows: I. Eocene--in which the placental mammals now on earth were represented by allied forms belonging to existing orders and families. Living orders and families appear; lemurs (Lemuridæ) in Europe and North America. Evidence found in fresh-water and marine strata; lignites. II. Miocene--in which the alliance between living and placental mammals is more close than before. Living genera appear; apes (Simiadæ) in Europe and North America. Evidence--fresh-water and marine strata; volcanic débris (Auvergne); lignites. III. Pliocene--in which living species of placental mammals appear. Living species appear; apes (Simiadæ) in Southern Europe. Evidence found in fresh-water and marine strata; volcanic débris (Auvergne). IV. Pleistocene--in which living species of placental mammals are more abundant than the extinct. Man appears; Anthropidæ; the palæolithic hunter; living species abundant. Evidence--refuse-heaps, contents of caves, river deposits, submarine forests, bowlder clay, moraines, marine sands, and shingle. V. Prehistoric--in which domestic animals and cultured fruits appear. Man abundant, domestic animals, cultivated fruits, spinning, weaving, pottery-making, mining, commerce; the neolithic, bronze, and iron stages of culture. Evidence--camps, habitations, tombs, refuse-heaps, surface accumulation, caves, alluvia, peat bogs, submarine forests, raised beaches. VI. Historic--in which the events are recorded in history. Evidence--documents, refuse-heaps, caves, tombs. The orders, families, genera, and species in the above summary, when traced forward in time, fall into the shape of a genealogical tree, with its trunk hidden in the secondary period, and its branchlets (the living species) passing upward from the Pliocene, a tree of life with living Mammalia for its fruits and foliage. Were the extinct species taken into account, it would be seen that they fill up the intervals separating one living form from another, and that they too grow more and more like the living forms as they approach nearer to the present day. It must be remembered that in the above definitions the fossil marsupials are purposely ignored, because they began their specialization in the secondary period, and had arrived in the Eocene at the stage which is marked by the presence of living genus--the opossum (Didelphys).