I think, however, we may still be allowed to entertain some doubts as to the reference to corals, more especially as the skeleton does not seem to have consisted of aragonite, but of ordinary calcite, like that of the Foraminifera. It is in any case a primitive form which seems to be dying out in the Lower Cambrian, and we may hope that it may be traced into the pre-Cambrian, and may form a link connecting the Palæozoic with the Eozoic faunas. In my description of it in "The Dawn of Life" in 1875, I used the following terms:--"To understand Archæocyathus, let us imagine an inverted cone of carbonate of lime from an inch or two to a foot in length, with its point planted in the mud in the bottom of the sea, while its open cup extends upward into the clear water. The lower part buried in the bottom is composed of an irregular network of thick calcareous plates, enclosing chambers communicating with one another. Above this, where the cup expands, its walls are made up of inner and outer plates, perforated with numerous round pores in vertical rows, and connected with each other by vertical partitions also perforated, so as to establish a free communication of the enclosed radiating chambers with each other, as well as with the water within and without. Such a structure might no doubt serve as a skeleton for a coral of somewhat peculiar internal structure, but it might just as well accommodate a protozoan with chambers for its sarcode, and pores for emission of pseudopods, both outwardly and by means of the interior cup, which in that case would represent a funnel like that of Carpenteria, or one of the tubes of Eozoon." [Footnote 58: Vol. xlv., 1889, pp. 125 _et seq._] On the whole, when we consider the magnitude and synthetic character of such forms as Cryptozoon, Receptaculites, and Archæocyathus, and their association with generalized types of Crustaceans and Brachiopods, we can scarcely fail to perceive that at the base of the Palæozoic we are leaving the reign of the higher marine invertebrates, and entering on a domain where lower and probably Protozoan forms must be dominant, and so are getting at least within calculable distance of the beginnings of life. * * * * * F. Pre-Geological Evolution. Reference is incidentally made in the text to the doctrine implied in the old notion of successive cataclysms and renewals of the earth, held by some ancient mythologies and philosophies, and revived in a slightly different form by Mr. Herbert Spencer, in connection with the requirements of the Darwinian evolution by natural selection. This primitive idea was illustrated at considerable length by Professor Poulton in his address as President of the Zoological Section of the British Association at its meeting in Liverpool (September, 1896). In this new and ably presented form, it deserves some notice as excluding the hope of our finding the beginnings of life in any geological formations at present known.