Among animals, instances of the same kind may be found in every sub-kingdom. The _Globigerina_ of the Atlantic soundings is identical with that which occurs in the chalk; and the casts of lower silurian _Foraminifera_, which Ehrenberg has recently described, seem to indicate the existence at that remote period of forms singularly like those which now exist. Among the corals, the palaeozoic _Tabulata_ are constructed on precisely the same type as the modern millepores; and if we turn to molluscs, the most competent malacologists fail to discover any generic distinction between the _Craniae_, _Lingulae_ and _Discinae_ of the silurian rocks and those which now live. Our existing _Nautilus_ has its representative species in every great formation, from the oldest to the newest; and _Loligo_, the squid of modern seas, appears in the lias, or at the bottom of the mesozoic series, in a form, at most, specifically different from its living congeners. In the great assemblage of annulose animals, the two highest classes, the insects and spider tribe, exhibit a wonderful persistency of type. The cockroaches of the carboniferous epoch are exceedingly similar to those which now run about our coal-cellars; and its locusts, termites and dragon-flies are closely allied to the members of the same groups which now chirrup about our fields, undermine our houses, or sail with swift grace about the banks of our sedgy pools. And, in like manner, the palaeozoic scorpions can only be distinguished by the eye of a naturalist from the modern ones. Finally, with respect to the _Vertebrata_, the same law holds good: certain types, such as those of the ganoid and placoid fishes, having persisted from the palaeozoic epoch to the present time without a greater amount of deviation from the normal standard than that which is seen within the limits of the group as it now exists. Even among the _Reptilia_—the class which exhibits the largest proportion of entirely extinct forms of any one type,—that of the _Crocodilia_, has persisted from at least the commencement of the mesozoic epoch up to the present time with so much constancy, that the amount of change which it exhibits may fairly, in relation to the time which has elapsed, be called insignificant. And the imperfect knowledge we have of the ancient mammalian population of our earth leads to the belief that certain of its types, such as that of the _Marsupialia_, have persisted with correspondingly little change through a similar range of time.