352 
NATURE 
[ Mar. e) 1873 
THE THEORY OF EVOLUTION IN GERMANY 
PROF. HAECKEL, of the University of Jena, may be re- 
garded as the most eminent living representative of the doc- 
trine of evolution in Germany. He has wona name for himself 
during the last ten years as the author of several remarkable 
works in various sections of Natural History ; specially should 
be mentioned his monograph on the Radio/aria (Berlin, 1862), 
which is, according to Huxley, one of the most solid and impor- 
tant contributions to zoology that have appeared for a long time. 
We owe also to him a monograph on the Monads (Journal de 
Jena pour -la Médecine, &c., 1868), the simplest of known 
organisms, and another on the Geryonide or Hydromeduse 
(Leipzig, 1865); a history of the development of the S/phono- 
phore, a work crowned by the Academy of Utrecht (1869) ; 
a paper on the Sarcode bodies of the RArzopoda (in the Four nal de 
Zoologie Scientifique, Leipzig, 1865); ‘‘ Considerations on the 
Division of Labour in Nature and among Men” (in the collec- 
tion of scientific treatises of Virchow and Holzendorff, 1869) ; 
and an essay on the ‘‘ Origin and the Genealogical Tree of the 
Human Race” (in the same collection, 1868 ; 2nd edition, 1870). 
There has just appeared a monograph on the Calcareous 
Sponges (See NATuRE, vol. vii. p. 279), on which the 
author has been engaged for five years, But his principal work 
is undoubtedly his ‘‘ Morphology of Organisms,” in which he 
has condensed the result of all his researches, and unfolded his 
views on Nature as a whole, its history, its constitution, and its 
development : it is a learned treatise on natural philosophy, in 
which the author has adopted out and out the system of 
Darwin. Indeed, on more than one point he goes much 
farther than his master, and does not shrink from any of 
the extreme consequences of principles which are simply stated 
by the English philosopher : it may with truth be said that he is 
more Darwinian than Darwin himself. He aims, in fact, at 
filling up the chasm which separates the organic and inorganic 
kingdoms, and is inclined to endow with life everything that has 
being, down to crystals and the smallest molecule of matter. 
Haeckel, with his comprehensive and philosophic mind, has 
more than once applied the theory of evolution to certain moral 
phenomena, and notably to politics, while Darwin has always 
shown considerable reserve in this direction. With respect, also, 
to the simian origin of man, he is much more explicit and pre- 
cise than the English naturalist. In short, as he does not con- 
fine himself simply to the exposition of theories and principles, 
as he seeks to recover the marks of development in the particular 
genealogy of animal and vegetable organisms, he is compelled to 
c mmit himself to a great number of hypotheses, whose boldness 
it is impossible to deny. We do not speak thus in the way of 
reproach ; we are none of those who think that science can live 
on experiment alone ; hypothesis has always preceded experi- 
ment, and has seemed to incite and throw light upon it; it is 
the torch of induction, and without it the human mind would be 
doomed to sterility. Goethe has truly said that bad hypotheses 
a-e better than none at all. All that we ought to insist on is, 
tiat a hypothesis be abandoned the moment it is found to con- 
t-adict certain facts, or when thejsame facts are more satisfactorily 
explained by a new hypothesis. One hypothesis may be better 
taan another in three points—(1) when it accounts for a greater 
number of facts ; (2) when it explains them by a smaller number 
of causes ; and (3) when it makes use only of known causes, and 
involves a smaller number of accessory hypotheses. This is why 
Darwinism is preferable to supematural hypotheses; it only 
applies to the whole round of natural phenomena causes which 
undoubtedly explain particular facts—natural selection, adapta- 
tion, and heredity. 
Haeckel has with justice observed that if the doctrine of evolu- 
tion has not yet been universally adopted, it ought to be attri- 
buted to the want of philosophic culture on the part of the 
great majority of contemporary naturalists ; and this reproach is 
specially deserved by France, where Darwinism has hitherto 
been much less understood thanin England and Germany. ‘‘ The 
numerous errors of speculative philosophy during the first thirty 
years of our century have brought such discredit on philosophy 
as a whole among the advocates of the exact and empirical 
method, that the latter at present labour under the strange de- 
lusion that the edifice of the natural sciences can be built up by 
means of facts alone without philosophic connection,—with 
* Translated from an article by M. Léon Dumont in La Réwue Scienti- 
“ique for January 25, 1873. 
simple notions unenlightened by any general conception. If a 
purely speculative work undisturbed by the indispensable con- 
ditions of empirical facts is a chimerical edifice whose inanity is 
exposed by the first experiment, on the other hand, a purely em- 
pirical doctrine, composed exclusively of facts, is only a formless 
heap, unworthy of the name of structure. Rough facts are not 
the only materials ; philosophic thought alone can rear them 
into a science. From this absence of the power of philoso- 
phising among naturalists proceed those gross mistakes in the 
elements of logic, that incapacity to draw the simplest conclusions, 
which are too clearly seen at the present day in all branches of 
the natural sciences, but particularly in zoology and botany.” * 
Haeckel has given a véswméof his theories as a whole 
in a series of lectures delivered at Jena in the Winter of 1867-68, 
These lectures have been re-published under the title of ‘* Natural 
History of Creation” (Berlin, 1868 ; 2nd ed. 1870), in a volume 
which has already gone through several editions. What follows 
is an analytical exposition of the most important parts of this 
work. The three sections which immediately follow contain the 
substance of the 12th, 13th, rqth, and 15th lectures, which 
form a division of Haeckel’s work under the title of ‘‘ Principal 
Characteristics and Fundamental Laws of the theory of Evolu- 
tion.” Haeckel discusses those facts of Embryology, Palzon- 
tology, and Chorology, or the geographical distribution of living 
beings, which are calculated to throw light upon the science of 
the development of species. 
Lmbryology 
It is astonishing how much ignorance even now prevails upon 
the embryonic development of man and animals generally. 
Just as the originator of the theory of evolution—Lamarck—had 
to wait half a century before Darwin came to rescue his doctrine 
from oblivion, and impart to it new life, so Wolff’s theory of 
Epigenesis, published in 1759, remained almost unknown till 
1803, when there appeared Oken’s ‘* History of the develop. 
ment of the Intestinal Canal.” It was only then that the study 
of Ontogenesis began to spread, and soon there appeared the 
classic researches of Pander (1817), and Baer (1819), The 
latter especially, in a book which marks an epoch (‘‘ History of 
the Development of Animals”), has established the most impor- 
tant facts of the embryology of the vertebrates with so much~™ 
intelligence and philosophic depth, that his doctrines have 
become the indispensable basis for the study of that group of 
animals to which men belong. 
At the outset of his existence, man, like every other 
animal organism, is only an egg, a simple little cell, whose 
diameter is only one-fourth of a millimetre at the most. It 
differs from the primordial cellule of the other mammalia only 
in its chemical constitution and the molecular composition of the 
albuminous matter of which the egg essentially consists. And 
yet these differences cannot be directly perceived by any means 
at our disposal ; but we are compelled by indirect conclusions 
to suppose their existence as the prime cause of the difference in 
individuals, The human egg encloses all the essential clemenis 
of a simple organic cellule: a protoplasm which bears the name 
of witellus, and a nucleus or germinal vesicle. This nucleus is a 
small sphere itself enclosing another nucleus much smaller still, 
the sucleolus ; exteriorly the protoplasm is enveloped by a mem- 
brane which is knowa by the name of zona pellucida. The eggs 
of many of the lower animals, as the greater part of the medusa, 
are on the contrary naked cells, which do’ not possess this 
envelope. 
As soon as the egg of the mammal is completely developed, 
it leaves the ovary and descends, by the narrow cenal of the 
oviduct, into the uterus, where, after fecundation, it becomes an 
embryo. This transformation is thus brought about :—the 
original cellule becomes divided into two cellules ; on the pri- 
mitive nucleolus are formed tivo new specks, and the nucleus 
becomes separated into two vesicles, each of which takes with 
it half of the protoplasm. The result of this process is that in 
the heart of the vitelline membrane, which alone is not divided, 
two cellules are found in juxtaposition, differing from the original 
only in being unenyeloped, Each of these new cellules is in 
its turn divided into two others, so as to form four, which in 
the same way become eight, these eight, sixteen, and so on ; these 
successive segmentations producing an agglomeration of cellules, 
in outward appearance resembling a mulberry. The further deve- 
lopment consists in these cells assuming the shape of a sac (vesicuda 
blastodermica), in the interior of which a Jiquid collects ; shortly, 
on a point of the wall which is composed of these cells 
* General Morphology, I. 63 ; II. 447. 
see 
a 
