This wonderful Palæozoic age was, however, but a temporary state of the earth. It passed away, and was replaced by the Mesozoic, emphatically the age of Reptiles, when animals of that type attained to colossal magnitude, to variety of function and structure, to diversity of habitat in sea and on land, altogether unexampled in their degraded descendants of modern times.... Strangely enough, with these reptilian lords appeared a few small and lowly mammals, forerunners of the coming age.[254] Birds also made their appearance. The Kainozoic, or Tertiary, is the age of Mammals and of Man. In it the great reptilian tyrants of the Mesozoic disappear, and are replaced on land and sea by mammals or beasts of the same orders with those now living, though differing as to genera and species. So greatly indeed did mammalian life abound in this period that in the middle part of the Tertiary most of the leading groups were represented by more numerous species than at present, while many types then existing have now no representatives. At the close of this great and wonderful procession of living beings comes Man himself--the last and crowning triumph of creation the head, thus far, of life on the earth. [Illustration: DIAGRAM ILLUSTRATING THE PROGRESS OF ORGANIC DEVELOPMENT. In the above Diagram the progress of Organic Development, as manifested in higher and higher types, is indicated by the increasing divergence of new forms from primitive simplicity of structure, represented by the medium line separating the vegetable and animal kingdoms. The _Supposed line of continuous Evolution,_ indicates the gradual course which should be taken by Development, on Darwinian or Spencerian principles, by accumulation of minute differences in successive generations, as contrasted with the abrupt and simultaneous appearance of highly differentiated types, as spoken of by palæontologists. [_To face page 227._]] It must be sufficient to quote one other remark:[255] There is no direct evidence that in the course of geological time one species has been gradually or suddenly changed into another.... On the other hand, we constantly find species replaced by others entirely new, and this without any transition. The two classes of facts are essentially different, though often confounded by evolutionists; and though it is possible to point out in the newer geological formations some genera and species allied to others which have preceded them, and to suppose that the later forms proceeded from the earlier, still, as the connecting links cannot be found, this is mere supposition, not scientific certainty. Further, it proceeds on the principle of arbitrary choice of certain forms out of many, without any evidence of genetic connexion. Having given a tabular view of Geological periods and Life-epochs, similar to those presented above, our author remarks:[256]