The geological table given at the close of this chapter may be of interest, as a careful consideration of it, and the foregoing facts, will show the real value of man in nature. That man is ascendent now, does not, in the light of experience, mean necessarily that he will by any means remain so. In the warm Champlain period, we know that brute mammals thrived and attained gigantic size, and, as Dana aptly remarks, "the great abundance of their remains and their conditions show that the climate and food were all that could have been desired." Yet the mastodon and the cave-bear have gone, together with countless other species which have become extinct, and, if science teaches anything at all, it tells us that nature delights in fostering one species at the expense of another. In the case of man, we most clearly see this. "For the historical succession of vertebrate fossils corresponds completely with the morphological scale which is revealed to us by comparative anatomy and ontology. After the Silurian fishes come the dipnoi of the Devonian period,--the Carboniferous amphibia, the Permian reptilia and the Mesozoic Mammals. Of these again, the lowest forms, the monotremes, appear first in the Triassic period; the marsupials in the Jurassic, and then the oldest placentals in the Cretaceous. Of the placentals, in turn, the first to appear in the oldest Tertiary period are the lowest primates, the prosimiæ, which are followed by the simiæ, in the Miocene. Of the carrhinæ, the cynopitheci precede the anthropomorpha; from one branch of the latter, during the Pliocene period, arises the apeman, without speech, and from him descends finally the speaking man. "Since the germ of the human embryo passes through the same chordula-stages as the germ of all other vertebrates; since it evolves, similarly, out of the two germinal layers of a gastrula, we infer by virtue of the biogenetic law, the early existence of corresponding ancestral forms. Most important of all is the fact that the human embryo, like that of all other animals, arises, originally, from a single cell, for this stem-cell--the impregnated egg cell--points, indubitably, to a corresponding unicellular ancestor, a primitive Laurentian protozoon." In the foregoing quotation, Haeckel clearly states what every geologist and embryologist plainly knows to be the truth, and in this case, as in all others, does it hold good: "Because truth is truth, to follow truth Were wisdom, in the scorn of consequence."