The Evolution of Man, vol 1 | Page 6

it was no light task to trace the
identity of this process of gastrulation in all the animals. It has been
done, however; and with this introduction the reader will be able to
follow the proof. The conclusion is important. If all animals pass
through the curious gastrula stage, it must be because they all had a
common ancestor of that nature. To this conjectural ancestor (it lived
before the period of fossilisation begins) Haeckel gives the name of the
Gastraea, and in the second volume we shall see a number of living
animals of this type ("gastraeads").
The line of argument is the same in the next chapter. After laborious
and careful research (though this stage is not generally admitted in the
same sense as the previous one), a fourth common stage was
discovered, and given the name of the Coelomula. The blastula had one
layer of cells, the blastoderm (derma = skin): the gastrula two layers,
the ectoderm ("outer skin") and entoderm ("inner skin"). Now a third
layer (mesoderm = middle skin) is formed, by the growth inwards of
two pouches or folds of the skin. The pouches blend together, and form
a single cavity (the body cavity, or coelom), and its two walls are two
fresh "germinal layers." Again, the identity of the process has to be
proved in all the higher classes of animals, and when this is done we
have another ancestral stage, the Coelomaea.
The remaining task is to build up the complex frame of the higher
animals--always showing the identity of the process (on which the

evolutionary argument depends) in enormously different conditions of
embryonic life--out of the four "germinal layers."
Chapter 1.
9 prepares us for the work by giving us a very clear account of the
essential structure of the back-boned (vertebrate) animal, and the
probable common ancestor of all the vertebrates (a small fish of the
lancelet type).

Chapters
1.11 to 1.14 then carry out the construction step by step. The work is
now simpler, in the sense that we leave all the invertebrate animals out
of account; but there are so many organs to be fashioned out of the four
simple layers that the reader must proceed carefully. In the second
volume each of these organs will be dealt with separately, and the
parallel will be worked out between its embryonic and its phylogenetic
(evolutionary) development. The general reader may wait for this for a
full understanding. But in the meantime the wonderful story of the
construction of all our organs in the course of a few weeks (the human
frame is perfectly formed, though less than two inches in length, by the
twelfth week) from so simple a material is full of interest. It would be
useless to attempt to summarise the process. The four chapters are
themselves but a summary of it, and the eighty fine illustrations of the
process will make it sufficiently clear. The last chapter carries the story
on to the point where man at last parts company with the anthropoid
ape, and gives a full account of the membranes or wrappers that enfold
him in the womb, and the connection with the mother.
In conclusion, I would urge the reader to consult, at his free library
perhaps, the complete edition of this work, when he has read the
present abbreviated edition. Much of the text has had to be condensed
in order to bring out the work at our popular price, and the beautiful
plates of the complete edition have had to be omitted. The reader will
find it an immense assistance if he can consult the library edition.
JOSEPH MCCABE.
Cricklewood, March, 1906.
***
HAECKEL'S CLASSIFICATION OF THE ANIMAL WORLD.
UNICELLULAR ANIMALS (PROTOZOA).

1. Unnucleated.
Bacteria. Protamoebae.
Monera.
2. Nucleated.
2A. Rhizopoda.
Amoebina. Radiolaria.
2B. Infusoria.
Flagellata. Ciliata.
3. Cell-Colonies.
Catallacta. Blastaeada.
MULTICELLULAR ANIMALS (METAZOA).
1. COELENTERIA, COELENTERATA, OR ZOOPHYTES. Animals
without body-cavity, blood or anus.
1A. Gastraeads.
Gastremaria. Cyemaria.
1B. Sponges.
Protospongiae. Metaspongiae.
1C. Cnidaria (Stinging Animals).
Hydrozoa. Polyps. Medusae.
1D. Platodes (Flat-Worms).
Platodaria. Turbellaria. Trematoda. Cestoda.
2. COELOMARIA OR BILATERALS. Animals with body-cavity and
anus, and generally blood.
2A. Vermalia (Worm-Like).
Rotatoria. Strongylaria. Prosopygia. Frontonia.
2B. Molluscs.
Cochlides. Conchades. Teuthodes.
2C. Articulates.
Annelida. Crustacea. Tracheata.
2D. Echinoderms.
Monorchonia. Pentorchonia.
2E. Tunicates.
Copelata. Ascidiae. Thalidiae.
2F. Vertebrates.
2F.1. Acrania-Lancelet (Without Skull).
2F.2. Craniota (With Skull).
2F.2A. Cyclostomes. ("Round-Mouthed").

2F.2B. Fishes.
Selachii. Ganoids. Teleosts. Dipneusts.
2F.2C. Amphibia.
2F.2D. Reptiles.
2F.2E. Birds.
2F.2F. Mammal.
Monotremes.
Marsupials.
Placentals:-- Rodents. Edentates. Ungulates. Cetacea. Sirenia.
Insectivora. Cheiroptera. Carnassia. Primates.
(This classification is given for the purpose of explaining Haeckel's use
of terms in this volume. The general reader should bear in mind that it
differs very considerably from more recent schemes of classification.
He should compare the scheme framed by Professor E. Ray Lankester.)
***
THE EVOLUTION OF MAN.