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                                                      "THROUGH THE EYE"
                                                                 SERIES

                               EVOLUTION




                       "THROUGH THE EYE" SERIES

                        _THE FIRST TWO VOLUMES_

                 EVOLUTION. By J. A. S. WATSON, B.Sc.

              THE CIVILIZATION OF THE ANCIENT EGYPTIANS.
                         By A. BOTHWELL GOSSE.

                    _Other Volumes in Preparation_

[Illustration: FIG. 1.--Tree illustrating the probable course of animal
                              evolution.]

                               EVOLUTION

                       BY J. A. S. WATSON, B.Sc.

                   [Illustration: THROUGH THE · EYE]

   _Published by_ T. C. & E. C. JACK, LTD. 35 & 36 PATERNOSTER ROW,
                     LONDON, E.C. AND AT EDINBURGH




                      _Printed in Great Britain_




                               CONTENTS


                               CHAPTER I

                                                                    PAGE

  THE EVIDENCE FOR EVOLUTION                                           1

                              CHAPTER II

  UNICELLULAR AND MULTICELLULAR ANIMALS                               23

                              CHAPTER III

  THE WORMS AND SOME OF THEIR POSTERITY                               58

                              CHAPTER IV

  THE EARLY VERTEBRATES AND THE FISHES                                79

                               CHAPTER V

  THE CONQUEST OF THE LAND                                           104

                              CHAPTER VI

  THE MAMMALS AND MAN                                                123

 For many of the illustrations the Publishers are indebted to the
 Deutsche Verlags-Anstalt (from Günther's _Vom Urtier zum Menschen_)
 and Herr Wilhelm Engelmann (from Haeckel's _Anthropogenie_).
 Acknowledgment is also made to Messrs. Watts & Co., London, the
 Publishers of the English Edition of Haeckel's _Anthropogenie_,
 entitled _The Evolution of Man_.




                               EVOLUTION




CHAPTER I

THE EVIDENCE FOR EVOLUTION


The idea of Evolution is an old one. It is older than the Darwinian
hypothesis; it is older than Lamarck, who published his particular
theory in 1809, the year that Darwin was born; it is older than Buffon
or Kant. In a fairly definite form it is as old as Aristotle. The
Evolution idea has thus itself evolved, and is the product of many
centuries of thought. Yet it was only the last generation that began to
give the idea serious consideration, and it is perhaps only the present
that has granted it any general measure of acceptance; and it was
Darwin who wrought this change, who raised the conception of Evolution
from the status of a vague speculative idea to that of a well-grounded
theory, which appeals to the majority of educated minds as satisfactory
and reasonable.

We do not here propose to sketch the development of the idea, either
before or after Darwin; but only, in the first place, to state the
grounds on which the belief in Evolution is based, and, in the second,
to trace roughly the lines along which animal Evolution has proceeded.
In the first few pages of this book, then, we shall endeavour to bring
forward some of the evidence on which the modern Evolution theory rests.

  +--------------+------------------+---------------+------------------+
  |              | First Appearance |Dominant Types.|                  |
  |              |    of Types.     |               |                  |
  +--------------+------------------+---------------+------------------+
  | Modern       |       ...       |  MAN          | } Post-tertiary, |
  | Diluvium     | Man              |    ...       | }  1/2 per cent. |
  +--------------+------------------+---------------+------------------+
  | Pliocene     |       ...       | }             | } Tertiary or    |
  | Miocene      | Monkeys          | } MAMMALS     | }  Cænozoic,     |
  | Oligocene    |       ...       | }             | } 2-1/2 per cent.|
  | Eocene       | Lemurs           | }             | }                |
  +--------------+------------------+---------------+------------------+
  | Cretaceous   | _Higher mammals_ | }             | } Secondary or   |
  | Jurassic     | { _Birds_        | } REPTILES    | }  Mesozoic,     |
  |              | { Marsupials     | }             | }  11 per cent.  |
  | Triassic     | _Monotremes_     | }             | }                |
  +--------------+------------------+---------------+------------------+
  | Permian      | _Reptiles_       |   AMPHIBIANS  | } Primary or     |
  | Carboniferous| _Amphibians_     | } FISHES      | }  Palæozoic,    |
  | Devonian     | _Lung fishes_    | }             | }  32 per cent.  |
  | Silurian     | _Lower fishes_   |     ...      | }                |
  +--------------+------------------+---------------+------------------+
  | Cambrian     |       ...       |     ...      | } Archäen, 54    |
  | Laurentian   |       ...       |     ...      | }  per cent.     |
  +--------------+------------------+---------------+------------------+

 FIG. 2.--Table showing the chronological succession of the stratified
 rocks, the subdivision of geological time, the approximate position of
 the earliest fossils of each of the main types of vertebrates, and the
 period of domination of each group.

As our first witness, we may call the rocks which constitute the outer
portion of the earth, and ask them to tell us what they remember of the
history of life upon the planet. We cannot hope for the whole truth
from them, for their memory is imperfect; and yet they can tell us a
great number of important facts.

[Illustration: THE EVOLUTION OF THE HORSE

FIG. 3.    From _The Guide to the American Museum of Natural History_.]

From the time when the world was sufficiently cooled for water to
condense on its surface, a continual process of unbuilding and
rebuilding of rocks has gone on. Wind and water, heat and cold have
laid their hands to the work, making sand and dust and gravel out of
solid stone, and these products of their labours have been carried
off to other places, laid down, and cemented together into new rocks.
We do not know the exact age of any particular rock that has been
made in this way, nor how