. Outlines of zoology. Zoology. 76 PAST HISTORY OF ANIMALS: though less perfectly, the modern crocodiles are linked by many intermediate forms to their extinct ancestors, for it is impossible not to call them by that name, and the modern horse to its entirely different progenitors. In short, as know- ledge increases, the evidence from Palaeontology becomes more and more complete. In a general way it is true that the simpler animals pre- cede the more complex in history as they do in structural rank, but the fact that all the great Invertebrate groups are represented in the oldest distinctly st
. Outlines of zoology. Zoology. 76 PAST HISTORY OF ANIMALS: though less perfectly, the modern crocodiles are linked by many intermediate forms to their extinct ancestors, for it is impossible not to call them by that name, and the modern horse to its entirely different progenitors. In short, as know- ledge increases, the evidence from Palaeontology becomes more and more complete. In a general way it is true that the simpler animals pre- cede the more complex in history as they do in structural rank, but the fact that all the great Invertebrate groups are represented in the oldest distinctly stratified and fossiliferous rocks—the Cambrian system—shows that this correspond- ence is only roughly true. To account for this, we must remember that the whole mass of the oldest rocks, known as Archaean or Pre-Cambrian, have been so pro- foundly altered, that, as a rule, only masses of marble and carbonaceous material are left to indicate that forms of life existed when these rocks were laid down. What these early forms of life were it seems impos- sible for us to find out, although recent discoveries, for instance, of "annelid tracks" in rocks of possible Pre- Cambrian age in Scotland, suggest that patient investigation may yet do much towards the solving of the problem. Extinction of types.—Some animals, such as some of the lamp-shells or Brachiopods, have persisted from almost the oldest ages till now, and most fossilised animals have modern representatives which we believe to be their actual descendants. That a species should disappear need not surprise us, if we believe in the " transformation " of one species into another. The disappearance is more apparent. Fig. 32.—Gradual transitions between Paludina Neumayri (a) and Paludina Hosrnesi (j).— From Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may n
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