Facts of the above nature—­and they could be greatly multiplied—­seem to point clearly to the existence of some law of progression, though we certainly are not yet in a position to formulate this law, or to indicate the precise manner in which it has operated.  Two considerations, also, must not be overlooked.  In the first place, there are various groups, some of them highly organised, which make their appearance at an extremely ancient date, but which continue throughout geological time almost unchanged, and certainly unprogressive.  Many of these “persistent types” are known—­such as various of the Foraminifera, the Linguloe, the Nautili, &c.; and they indicate that under given conditions, at present unknown to us, it is possible for a life-form to subsist for an almost indefinite period without any important modification of its structure.  In the second place, whilst the facts above mentioned point to some general law of progression of the great zoological groups, it cannot be asserted that the primeval types of any given group are necessarily “lower,” zoologically speaking, than their modern representatives.  Nor does this seem to be at all necessary for the establishment of the law in question.  It cannot be asserted, for example, that the Ganoid and Placoid Fishes of the Upper Silurian are in themselves less highly organised than their existing representatives; nor can it even be asserted that the Ganoid and Placoid orders are low groups of the class Pisces.  On the contrary, they are high groups; but then it must be remembered that these are probably not really the first Fishes, and that if we meet with Fishes at some future time in the Lower Silurian or Cambrian, these may easily prove to be representatives of the lower orders of the class.  This question cannot be further entered into here, as its discussion could be carried out to an almost unlimited length; but whilst there are facts pointing both ways, it appears that at present we are not justified in asserting that the earlier types of each group—­so far as these are known to us, or really are without predecessors—­are necessarily or invariably more “degraded” or “embryonic” in their structure than their more modern representatives.

It remains to consider very briefly how far Palaeontology supports the doctrine of “Evolution,” as it is called; and this, too, is a question of almost infinite dimensions, which can but be glanced at here.  Does Palaeontology teach us that the almost innumerable kinds of animals and plants which we know to have successively flourished upon the earth in past times were produced separately and wholly independently of each other, at successive periods? or does it point to the theory that a large number of these supposed distinct forms, have been in reality produced by the slow modification of a comparatively small number of primitive types?  Upon the whole, it must be unhesitatingly replied that the evidence of Palaeontology