LIST OF ILLUSTRATIONS.
PORTRAIT OF ERNST HAECKEL FROM THE PAINTING BY FRANZ VON LEUBACH, 1899
(REPRODUCED BY "JUGEND").
FIGURE 1.1. THE HUMAN OVUM.
FIGURE 1.2. STEM-CELL OF AN ECHINODERM.
FIGURE 1.3. THREE EPITHELIAL CELLS.
FIGURE 1.4. FIVE SPINY OR GROOVED CELLS.
FIGURE 1.5. TEN LIVER-CELLS.
FIGURE 1.6. NINE STAR-SHAPED BONE-CELLS.
FIGURE 1.7. ELEVEN STAR-SHAPED CELLS.
FIGURE 1.8. UNFERTILISED OVUM OF AN ECHINODERM.
FIGURE 1.9. A LARGE BRANCHING NERVE-CELL.
FIGURE 1.10. BLOOD-CELLS.
FIGURE 1.11. INDIRECT OR MITOTIC CELL-DIVISION.
FIGURE 1.12. MOBILE CELLS.
FIGURE 1.13. OVA OF VARIOUS ANIMALS.
FIGURE 1.14. THE HUMAN OVUM.
FIGURE 1.15. FERTILISED OVUM OF HEN.
FIGURE 1.16. A CREEPING AMOEBA.
FIGURE 1.17. DIVISION OF AN AMOEBA.
FIGURE 1.18. OVUM OF A SPONGE.
FIGURE 1.19. BLOOD-CELLS, OR PHAGOCYTES.
FIGURE 1.20. SPERMIA OR SPERMATOZOA.
FIGURE 1.21. SPERMATOZOA OF VARIOUS ANIMALS.
FIGURE 1.22. A SINGLE HUMAN SPERMATOZOON.
FIGURE 1.23. FERTILISATION OF THE OVUM.
FIGURE 1.24. IMPREGNATED ECHINODERM OVUM.
FIGURE 1.25. IMPREGNATION OF THE STAR-FISH OVUM.
FIGURES 1.26 AND 1.27. IMPREGNATION OF SEA-URCHIN OVUM.
FIGURE 1.28. STEM-CELL OF A RABBIT.
FIGURE 1.29. GASTRULATION OF A CORAL.
FIGURE 1.30. GASTRULA OF A GASTRAEAD.
FIGURE 1.31. GASTRULA OF A WORM.
FIGURE 1.32. GASTRULA OF AN ECHINODERM.
FIGURE 1.33. GASTRULA OF AN ARTHROPOD.
FIGURE 1.34. GASTRULA OF A MOLLUSC.
FIGURE 1.35. GASTRULA OF A VERTEBRATE.
FIGURE 1.36. GASTRULA OF A LOWER SPONGE.
FIGURE 1.37. CELLS FROM THE PRIMARY GERMINAL LAYERS.
FIGURE 1.38. GASTRULATION OF THE AMPHIOXUS.
FIGURE 1.39. GASTRULA OF THE AMPHIOXUS.
FIGURE 1.40. CLEAVAGE OF THE FROG'S OVUM.
FIGURES 1.41 TO 1.44. SECTIONS OF FERTILISED TOAD OVUM.
FIGURES 1.45 TO 1.48. GASTRULATION OF THE SALAMANDER.
FIGURE 1.49. SEGMENTATION OF THE LAMPREY.
FIGURE 1.50. GASTRULATION OF THE LAMPREY.
FIGURE 1.51. GASTRULATION OF CERATODUS.
FIGURE 1.52. OVUM OF A DEEP-SEA BONY FISH.
FIGURE 1.53. SEGMENTATION OF A BONY FISH.
FIGURE 1.54. DISCOID GASTRULA OF A BONY FISH.
FIGURES 1.55 AND 1.56. SECTIONS OF BLASTULA OF SHARK.
FIGURE 1.57. DISCOID SEGMENTATION OF BIRD'S OVUM.
FIGURES 1.58 TO 1.61. GASTRULATION OF THE BIRD.
FIGURE 1.62. GERMINAL DISK OF THE LIZARD.
FIGURES 1.63 AND 1.64. GASTRULATION OF THE OPOSSUM.
FIGURES 1.65 TO 1.67. GASTRULATION OF THE OPOSSUM.
FIGURES 1.68 TO 1.71. GASTRULATION OF THE RABBIT.
FIGURE 1.72. GASTRULA OF THE PLACENTAL MAMMAL.
FIGURE 1.73. GASTRULA OF THE RABBIT.
FIGURES 1.74 AND 1.75. DIAGRAM OF THE FOUR SECONDARY GERMINAL LAYERS.
FIGURES 1.76 AND 1.77. COELOMULA OF SAGITTA.
FIGURE 1.78. SECTION OF YOUNG SAGITTA.
FIGURES 1.79 AND 1.80. SECTION OF AMPHIOXUS-LARVAE.
FIGURES 1.81 AND 1.82. SECTION OF AMPHIOXUS-LARVAE.
FIGURES 1.83 AND 1.84. CHORDULA OF THE AMPHIOXUS.
FIGURES 1.85 AND 1.86. CHORDULA OF THE AMPHIBIA.
FIGURES 1.87 AND 1.88. SECTION OF COELOMULA-EMBRYOS OF VERTEBRATES.
FIGURES 1.89 AND 1.90. SECTION OF COELOMULA-EMBRYO OF TRITON.
FIGURE 1.91. DORSAL PART OF THREE TRITON-EMBRYOS.
FIGURE 1.92. CHORDULA-EMBRYO OF A BIRD.
FIGURE 1.93. VERTEBRATE-EMBRYO OF A BIRD.
FIGURES 1.94 AND 1.95. SECTION OF THE PRIMITIVE STREAK OF A CHICK.
FIGURE 1.96. SECTION OF THE PRIMITIVE GROOVE OF A RABBIT.
FIGURE 1.97. SECTION OF PRIMITIVE MOUTH OF A HUMAN EMBRYO.
FIGURES 1.98 TO 1.102. THE IDEAL PRIMITIVE VERTEBRATE.
FIGURE 1.103. REDUNDANT MAMMARY GLANDS.
FIGURE 1.104. A GREEK GYNECOMAST.
FIGURE 1.105. SEVERANCE OF THE DISCOID MAMMAL EMBRYO.
FIGURES 1.106 AND 1.107. THE VISCERAL EMBRYONIC VESICLE.
FIGURE 1.108. FOUR ENTODERMIC CELLS.
FIGURE 1.109. TWO ENTODERMIC CELLS.
FIGURES 1.110 TO 1.114. OVUM OF A RABBIT.
FIGURES 1.115 TO 1.118. EMBRYONIC VESICLE OF A RABBIT.
FIGURE 1.119. SECTION OF THE GASTRULA OF FOUR VERTEBRATES.
FIGURES 1.120 TO 1.123. EMBRYONIC SHIELD OF A RABBIT.
FIGURE 1.124. COELOMULA OF THE AMPHIOXUS.
FIGURE 1.125. CHORDULA OF A FROG.
FIGURE 1.126. SECTION OF FROG-EMBRYO.
FIGURES 1.127 AND 1.128. DORSAL SHIELD OF A CHICK.
FIGURE 1.129. SECTION OF HIND END OF A CHICK.
FIGURE 1.130. GERMINAL AREA OF THE RABBIT.
FIGURE 1.131. EMBRYO OF THE OPOSSUM.
FIGURE 1.132. EMBRYONIC SHIELD OF THE RABBIT.
FIGURE 1.133. HUMAN EMBRYO AT THE SANDAL-STAGE.
FIGURE 1.134. EMBRYONIC SHIELD OF RABBIT.
FIGURE 1.135. EMBRYONIC SHIELD OF OPOSSUM.
FIGURE 1.136. EMBRYONIC DISK OF A CHICK.
FIGURE 1.137. EMBRYONIC DISK OF A HIGHER VERTEBRATE.
FIGURES 1.138 TO 1.142. SECTIONS OF MATURING MAMMAL EMBRYO.
FIGURES 1.143 TO 1.146. SECTIONS OF EMBRYONIC CHICKS.
FIGURE 1.147. SECTION OF EMBRYONIC CHICK.
FIGURE 1.148. SECTION OF FORE-HALF OF CHICK-EMBRYO.
FIGURES 1.149 AND 1.150. SECTIONS OF HUMAN EMBRYOS.
FIGURE 1.151. SECTION OF A SHARK-EMBRYO.
FIGURE 1.152. SECTION OF A DUCK-EMBRYO.
FIGURES 1.153 TO 1.155. SOLE-SHAPED EMBRYONIC DISK OF CHICK.
FIGURES 1.156 AND 1.157. EMBRYO OF THE AMPHIOXUS.
FIGURES 1.158 TO 1.160. EMBRYO OF THE AMPHIOXUS.
FIGURES 1.161 AND 1.162. SECTIONS OF SHARK-EMBRYOS.
FIGURE 1.163. SECTION OF A TRITON-EMBRYO.
FIGURES 1.164 TO 1.166. VERTEBRAE.
FIGURE 1.167. HEAD OF A SHARK-EMBRYO.
FIGURES 1.168 AND 1.169. HEAD OF A CHICK-EMBRYO.
FIGURE 1.170. HEAD OF A DOG-EMBRYO.
FIGURE 1.171. HUMAN EMBRYO OF THE FOURTH WEEK.
FIGURE 1.172. SECTION OF SHOULDER OF CHICK-EMBRYO.
FIGURE 1.173. SECTION OF PELVIC REGION OF CHICK-EMBRYO.
FIGURE 1.174. DEVELOPMENT OF THE LIZARD'S LEGS.
FIGURE 1.175. HUMAN-EMBRYO FIVE WEEKS OLD.
FIGURES 1.176 TO 1.178. EMBRYOS OF THE BAT.
FIGURE 1.179. HUMAN EMBRYOS.
FIGURE 1.180. HUMAN EMBRYO OF THE FOURTH WEEK.
FIGURE 1.181. HUMAN EMBRYO OF THE FIFTH WEEK.
FIGURE 1.182. SECTION OF TAIL OF HUMAN EMBRYO.
FIGURES 1.183 AND 1.184. HUMAN EMBRYO DISSECTED.
FIGURE 1.185. MISS JULIA PASTRANA.
FIGURES 1.186 TO 1.190. HUMAN EMBRYOS.
FIGURE 1.191. HUMAN EMBRYOS OF SIXTEEN TO EIGHTEEN DAYS.
FIGURES 1.192 AND 1.193. HUMAN EMBRYO OF FOURTH WEEK.
FIGURE 1.194. HUMAN EMBRYO WITH ITS MEMBRANES.
FIGURE 1.195. DIAGRAM OF THE EMBRYONIC ORGANS.
FIGURE 1.196. SECTION OF THE PREGNANT WOMB.
FIGURE 1.197. EMBRYO OF SIAMANG-GIBBON.
FIGURE 1.198. SECTION OF PREGNANT WOMB.
FIGURES 1.199 AND 1.200. HUMAN FOETUS AND PLACENTA.
FIGURE 1.201. VITELLINE VESSELS IN GERMINATIVE AREA.
FIGURE 1.202. BOAT-SHAPED EMBRYO OF THE DOG.
FIGURE 1.203. LAR OR WHITE-HANDED GIBBON.
FIGURE 1.204. YOUNG ORANG.
FIGURE 1.205. WILD ORANG.
FIGURE 1.206. BALD-HEADED CHIMPANZEE.
FIGURE 1.207. FOETAL MEMBRANES AND CIRCULATION.
FIGURE 1.208. FEMALE GORILLA.
FIGURE 1.209. MALE GIANT-GORILLA.
GLOSSARY.
ACRANIA: animals without skull (cranium).
ANTHROPOGENY: the evolution (genesis) of man (anthropos).
ANTHROPOLOGY: the science of man.
ARCHI-: (in compounds) the first or typical--as, archi-cytula,
archi-gastrula, etc.
BIOGENY: the science of the genesis of life (bios).
BLAST-: (in compounds) pertaining to the early embryo (blastos = a
bud); hence:--
Blastoderm: skin (derma) or enclosing layer of the embryo.
Blastosphere: the embryo in the hollow sphere stage.
Blastula: same as preceding.
Epiblast: the outer layer of the embryo (ectoderm).
Hypoblast: the inner layer of the embryo (endoderm).
BRANCHIAL: pertaining to the gills (branchia).
CARYO-: (in compounds) pertaining to the nucleus (caryon); hence:--
Caryokineses: the movement of the nucleus.
Caryolysis: dissolution of the nucleus.
Caryoplasm: the matter of the nucleus.
CENTROLECITHAL: see under LECITH-.
CHORDARIA and CHORDONIA: animals with a dorsal chord or back-bone.
COELOM or COELOMA: the body-cavity in the embryo; hence:--
Coelenterata: animals without a body-cavity.
Coelomaria: animals with a body-cavity.
Coelomation: formation of the body-cavity.
CYTO-: (in compounds) pertaining to the cell (cytos); hence:--
Cytoblast: the nucleus of the cell.
Cytodes: cell-like bodies, imperfect cells.
Cytoplasm: the matter of the body of the cell.
Cytosoma: the body (soma) of the cell.
CRYPTORCHISM: abnormal retention of the testicles in the body.
DEUTOPLASM: see PLASM.
DUALISM: the belief in the existence of two entirely distinct
principles (such as matter and spirit).
DYSTELEOLOGY: the science of those features in organisms which refute
the "design-argument."
ECTODERM: the outer (ekto) layer of the embryo.
ENTODERM: the inner (ento) layer of the embryo.
EPIDERM: the outer layer of the skin.
EPIGENESIS: the theory of gradual development of organs in the embryo.
EPIPHYSIS: the third or central eye in the early vertebrates.
EPISOMA: see SOMA.
EPITHELIA: tissues covering the surface of parts of the body (such as
the mouth, etc.)
GONADS: the sexual glands.
GONOCHORISM: separation of the male and female sexes.
GONOTOMES: sections of the sexual glands.
GYNECOMAST: a male with the breasts (masta) of a woman (gyne).
HEPATIC: pertaining to the liver (hepar).
HOLOBLASTIC: embryos in which the animal and vegetal cells divide
equally (holon = whole).
HYPERMASTISM: the possession of more than the normal breasts (masta).
HYPOBRANCHIAL: underneath (hypo) the gills.
HYPOPHYSIS: sensitive-offshoot from the brain in the vertebrate.
HYPOSOMA: see SOMA.
LECITH-: pertaining to the yelk (lecithus); hence:--
Centrolecithal: eggs with the yelk in the centre.
Lecithoma: the yelk-sac.
Telolecithal: eggs with the yelk at one end.
MEROBLASTIC: cleaving in part (meron) only.
META-: (in compounds) the "after" or secondary stage; hence:--
Metagaster: the secondary or permanent gut (gaster).
Metaplasm: secondary or differentiated plasm.
Metastoma: the secondary or permanent mouth (stoma).
Metazoa: the higher or later animals, made up of many cells.
Metovum: the mature or advanced ovum.
METAMERA: the segments into which the embryo breaks up.
METAMERISM: the segmentation of the embryo.
MONERA: the most primitive of the unicellular organisms.
MONISM: belief in the fundamental unity of all things.
MORPHOLOGY: the science of organic forms (generally equivalent to
anatomy).
MYOTOMES: segments into which the muscles break up.
NEPHRA: the kidneys; hence:--
Nephridia: the rudimentary kidney-organs.
Nephrotomes: the segments of the developing kidneys.
ONTOGENY: the science of the development of the individual (generally
equivalent to embryology).
PERIGENESIS: the genesis of the movements in the vital particles.
PHAGOCYTES: cells that absorb food (phagein = to eat).
PHYLOGENY: the science of the evolution of species (phyla).
PLANOCYTES: cells that move about (planein).
PLASM: the colloid or jelly-like matter of which organisms are
composed; hence:--
Caryoplasm: the matter of the nucleus (caryon).
Cytoplasm: the matter of the body of the cell.
Deutoplasm: secondary or differentiated plasm.
Metaplasm: secondary or differentiated plasm.
Protoplasm: primitive or undifferentiated plasm.
PLASSON: the simplest form of plasm.
PLASTIDULES: small particles of plasm.
POLYSPERMISM: the penetration of more than one sperm-cell into the ovum.
PRO- or PROT: (in compounds) the earlier form (opposed to META); hence:--
Prochorion: the first form of the chorion.
Progaster: the first or primitive stomach.
Pronephridia: the earlier form of the kidneys.
Prorenal: the earlier form of the kidneys.
Prostoma: the first or primitive mouth.
Protists: the earliest or unicellular organisms.
Provertebrae: the earliest phase of the vertebrae.
Protophyta: the primitive or unicellular plants.
Protoplasm: undifferentiated plasm.
Protozoa: the primitive or unicellular animals.
RENAL: pertaining to the kidneys (renes).
SCATULATION: packing or boxing-up (scatula = a box).
SCLEROTOMES: segments into which the primitive skeleton falls.
SOMA: the body; hence:--
Cytosoma: the body of the cell (cytos).
Episoma: the upper or back-half of the embryonic body.
Somites: segments of the embryonic body.
Hyposoma: the under or belly-half of the embryonic body.
TELEOLOGY: the belief in design and purpose (telos) in nature.
TELOLECITHAL: see LECITH-.
UMBILICAL: pertaining to the navel (umbilicus).
VITELLINE: pertaining to the yelk (vitellus).
***
PREFACE.
[BY JOSEPH MCCABE.]
The work which we now place within the reach of every reader of the
English tongue is one of the finest productions of its distinguished
author. The first edition appeared in 1874. At that time the
conviction of man's natural evolution was even less advanced in
Germany than in England, and the work raised a storm of controversy.
Theologians--forgetting the commonest facts of our individual
development--spoke with the most profound disdain of the theory that a
Luther or a Goethe could be the outcome of development from a tiny
speck of protoplasm. The work, one of the most distinguished of them
said, was "a fleck of shame on the escutcheon of Germany." To-day its
conclusion is accepted by influential clerics, such as the Dean of
Westminster, and by almost every biologist and anthropologist of
distinction in Europe. Evolution is not a laboriously reached
conclusion, but a guiding truth, in biological literature to-day.
There was ample evidence to substantiate the conclusion even in the
first edition of the book. But fresh facts have come to light in each
decade, always enforcing the general truth of man's evolution, and at
times making clearer the line of development. Professor Haeckel
embodied these in successive editions of his work. In the fifth
edition, of which this is a translation, reference will be found to
the very latest facts bearing on the evolution of man, such as the
discovery of the remarkable effect of mixing human blood with that of
the anthropoid ape. Moreover, the ample series of illustrations has
been considerably improved and enlarged; there is no scientific work
published, at a price remotely approaching that of the present
edition, with so abundant and excellent a supply of illustrations.
When it was issued in Germany, a few years ago, a distinguished
biologist wrote in the Frankfurter Zeitung that it would secure
immortality for its author, the most notable critic of the idea of
immortality. And the Daily Telegraph reviewer described the English
version as a "handsome edition of Haeckel's monumental work," and "an
issue worthy of the subject and the author."
The influence of such a work, one of the most constructive that
Haeckel has ever written, should extend to more than the few hundred
readers who are able to purchase the expensive volumes of the original
issue. Few pages in the story of science are more arresting and
generally instructive than this great picture of "mankind in the
making." The horizon of the mind is healthily expanded as we follow
the search-light of science down the vast avenues of past time, and
gaze on the uncouth forms that enter into, or illustrate, the line of
our ancestry. And if the imagination recoils from the strange and
remote figures that are lit up by our search-light, and hesitates to
accept them as ancestral forms, science draws aside another veil and
reveals another picture to us. It shows us that each of us passes, in
our embryonic development, through a series of forms hardly less
uncouth and unfamiliar. Nay, it traces a parallel between the two
series of forms. It shows us man beginning his existence, in the ovary
of the female infant, as a minute and simple speck of jelly-like
plasm. It shows us (from analogy) the fertilised ovum breaking into a
cluster of cohering cells, and folding and curving, until the
limb-less, head-less, long-tailed foetus looks like a worm-shaped
body. It then points out how gill-slits and corresponding
blood-vessels appear, as in a lowly fish, and the fin-like extremities
bud out and grow into limbs, and so on; until, after a very clear
ape-stage, the definite human form emerges from the series of
transformations.
It is with this embryological evidence for our evolution that the
present volume is concerned. There are illustrations in the work that
will make the point clear at a glance. Possibly TOO clear; for the
simplicity of the idea and the eagerness to apply it at every point
have carried many, who borrow hastily from Haeckel, out of their
scientific depth. Haeckel has never shared their errors, nor
encouraged their superficiality. He insists from the outset that a
complete parallel could not possibly be expected. Embryonic life
itself is subject to evolution. Though there is a general and
substantial law--as most of our English and American authorities
admit--that the embryonic series of forms recalls the ancestral series
of forms, the parallel is blurred throughout and often distorted. It
is not the obvious resemblance of the embryos of different animals,
and their general similarity to our extinct ancestors in this or that
organ, on which we must rest our case. A careful study must be made of
the various stages through which all embryos pass, and an effort made
to prove their real identity and therefore genealogical relation.
This is a task of great subtlety and delicacy. Many scientists have
worked at it together with Professor Haeckel--I need only name our own
Professor Balfour and Professor Ray Lankester--and the scheme is
fairly complete. But the general reader must not expect that even so
clear a writer as Haeckel can describe these intricate processes
without demanding his very careful attention. Most of the chapters in
the present volume (and the second volume will be less difficult) are
easily intelligible to all; but there are points at which the line of
argument is necessarily subtle and complex. In the hope that most
readers will be induced to master even these more difficult chapters,
I will give an outline of the characteristic argument of the work.
Haeckel's distinctive services in regard to man's evolution have been:
1. The construction of a complete ancestral tree, though, of course,
some of the stages in it are purely conjectural, and not final.
2. The tracing of the remarkable reproduction of ancestral forms in
the embryonic development of the individual. Naturally, he has not
worked alone in either department.
The second volume of this work will embody the first of these two
achievements; the present one is mainly concerned with the latter. It
will be useful for the reader to have a synopsis of the argument and
an explanation of some of the chief terms invented or employed by the
author.
The main theme of the work is that, in the course of their embryonic
development, all animals, including man, pass roughly and rapidly
through a series of forms which represents the succession of their
ancestors in the past. After a severe and extensive study of embryonic
phenomena, Haeckel has drawn up a "law" (in the ordinary scientific
sense) to this effect, and has called it "the biogenetic law," or the
chief law relating to the evolution (genesis) of life (bios). This law
is widely and increasingly accepted by embryologists and zoologists.
It is enough to quote a recent declaration of the great American
zoologist, President D. Starr Jordan: "It is, of course, true that the
life-history of the individual is an epitome of the life-history of
the race"; while a distinguished German zoologist (Sarasin) has
described it as being of the same use to the biologist as spectrum
analysis is to the astronomer.
But the reproduction of ancestral forms in the course of the embryonic
development is by no means always clear, or even always present. Many
of the embryonic phases do not recall ancestral stages at all. They
may have done so originally, but we must remember that the embryonic
life itself has been subject to adaptive changes for millions of
years. All this is clearly explained by Professor Haeckel. For the
moment, I would impress on the reader the vital importance of fixing
the distinction from the start. He must thoroughly familiarise himself
with the meaning of five terms.
BIOGENY is the development of life in general (both in the individual
and the species), or the sciences describing it.
ONTOGENY is the development (embryonic and post-embryonic) of the
individual (on), or the science describing it.
PHYLOGENY is the development of the race or stem (phulon), or the
science describing it.
Roughly, ontogeny may be taken to mean embryology, and phylogeny what
we generally call evolution.
Further, the embryonic phenomena sometimes reproduce ancestral forms,
and they are then called PALINGENETIC (from palin = again): sometimes
they do not recall ancestral forms, but are later modifications due to
adaptation, and they are then called CENOGENETIC (from kenos = new or
foreign).
These terms are now widely used, but the reader of Haeckel must
understand them thoroughly.
The first five chapters are an easy account of the history of
embryology and evolution. The sixth and seventh give an equally clear
account of the sexual elements and the process of conception. But some
of the succeeding chapters must deal with embryonic processes so
unfamiliar, and pursue them through so wide a range of animals in a
brief space, that, in spite of the 200 illustrations, they will offer
difficulty to many a reader. As our aim is to secure, not a
superficial acquiescence in conclusions, but a fair comprehension of
the truths of science, we have retained these chapters. However, I
will give a brief and clear outline of the argument, so that the
reader with little leisure may realise their value.
When the animal ovum (egg-cell) has been fertilised, it divides and
subdivides until we have a cluster of cohering cells, externally not
unlike a raspberry or mulberry. This is the morula (= mulberry) stage.
The cluster becomes hollow, or filled with fluid in the centre, all
the cells rising to the surface. This is the blastula (hollow ball)
stage. One half of the cluster then bends or folds in upon the other,
as one might do with a thin indiarubber ball, and we get a vase-shaped
body with hollow interior (the first stomach, or "primitive gut"), an
open mouth (the first or "primitive mouth"), and a wall composed of
two layers of cells (two "germinal layers"). This is the gastrula
(stomach) stage, and the process of its formation is called
gastrulation. A glance at the illustration (Figure 1.29) will make
this perfectly clear.
So much for the embryonic process in itself. The application to
evolution has been a long and laborious task. Briefly, it was
necessary to show that ALL the multicellular animals passed through
these three stages, so that our biogenetic law would enable us to
recognise them as reminiscences of ancestral forms. This is the work
of Chapters 1.8 and 1.9. The difficulty can be realised in this way:
As we reach the higher animals the ovum has to take up a large
quantity of yelk, on which it may feed in developing. Think of the
bird's "egg." The effect of this was to flatten the germ (the morula
and blastula) from the first, and so give, at first sight, a totally
different complexion to what it has in the lowest animals. When we
pass the reptile and bird stage, the large yelk almost disappears (the
germ now being supplied with blood by the mother), but the germ has
been permanently altered in shape, and there are now a number of new
embryonic processes (membranes, blood-vessel connections, etc.). Thus
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.