630 
NATURE 
[ Oct, 28, 1886 
continuity of the germ-plasma, but it was one which in the 
former memoir was only lightly touched upon. 
A large part of the contents of the present memoir was de- 
livered as a lecture at a meeting of the German Naturalists’ 
Association at Strasburg in September 1885; but numerous 
alterations and additions have been made, and six appendixes 
on special points have been added. 
At the outset, special attention is drawn to the essential dif- 
ference between ‘‘those special new characters which are cor- 
rectly to be included under the term ‘acquired,’ ” and the much 
broader class of new characters generally. Only those new 
characters can be termed ‘‘ acquired” the origin of which is due 
to external influences, and not those which depend on the myste- 
rious collaboration of the different tendencies of heredity which 
meet one another in the impregnated germ. These latter are 
not acquired, but ‘‘ inherited.” If, as the author holds, acquired 
characters are incapable of being transmitted to the progeny by 
the parent, then a much wider field of action must be ascribed 
to the processes of selection in the transformation of species than 
hitherto, since the modifying influences of external conditions 
being confined to the individual, can, in the vast majority of 
instances, have no effect on the tran formation of <pecies. 
After discussing Nageli’s postulation of the existence in or- 
ganisms of a special internal modifying force to account for the 
phenomena of adaptation, and showing that such a force has no 
existence at all, and that there are no reasons or justification for 
assuming it, the author dwells on the adequacy of the theory of 
selection to account for the facts. He insists specially on the 
necessity that the changes occurring during the transformation 
of a species, both in the organism itself and in the conditions of 
existence, shall take place by,the smallest possible stages with 
the utmost slowness, so that at no moment of the entire process 
of transformation shall the species remain inadequately adapted 
to its conditions. 
The possibility of the transmission of acquired characters 
being excluded, it is assumed that, in the case of all animals and 
plants which are reproduced by real germs, only those characters 
can be transmitted to a succeeding generation which were 
already present in the germ at the time of its formation. 
On the theory of the continuity of the germ-plasma, a 
certain minimum of the active substance of the germ, the germ- 
plasma, always remains unchanged when the germ develops into 
the organisn, and this remains of the germ-plasma becomes the 
basis from which the germ-cells of the new organism are formed. 
Thus there is a continuity of germ-plasma from one generation 
to another, and the impossibility of the transmission of acquired 
characters follows directly from this position, since the molecular 
structure of the germ-plasma is already determined within the 
embryo. 
There are no facts which really prove that acquired characters 
can be inherited, although many attempts have been made to 
render such a supposition plausible. On the contrary, the 
evidence against ic is abundant. The children of highly-civilised 
races of mankind, when brought up in isolation, show no trace 
of a language, and the results of experiments made on plants 
tell markedly on the same side. 
‘Twenty-two pages of appendixes are devoted to demonstrating 
this most important position—the influence of which on future 
speculation with regard to organic evolution can hardly be over- 
estimated—that acquired peculiarities are not hereditarily trans- 
missible. Only some of the statements with regard to the 
familiar instance of Brown-Séquard’s hereditarily epileptic 
guinea-pigs can here be given. 
Brown: Séquard, as is well known, produced artificially epi- 
lepsy in guinea-pigs by means of section of certain parts of the 
central or even peripheral nervous system in the living healthy 
animals. The progeny of these guinea-pigs inherited the disease 
of the parents. The experiments were repeated by Obersteiner, 
and there is no doubt of the fact. Still, urges our author, this 
Is not to be taken as a proof that acquired peculiarities can be 
inherited, Epilepsy is no morphological peculiarity, but a 
-disease. 
If there were found in the epileptic offspring a distinct and 
evident morphological alteration in the nervous structures caused 
by and corresponding with that produced by injury in the parent, 
and which was at the same time the cause of the epilepsy in the 
offspring, then the question of the actual transmission of an 
-acquired morphological peculiarity might be justly raised. 
That such is the case is, however, not only not proved, but 
very improbable. What is certain is that many of the young of 
such artificially epileptic parents are small and feeble, and often 
die early ; others show deformities and sores on various parts of 
their bodies. In rare instances certain of these young exhibit 
epileptic symptoms. Two only out of thirty-two young of 
epileptic parents showed the symptoms, and these soon died, 
having but very little vitality. 
The facts may be fairly expressed by stating that the guinea- 
pigs artificially rendered epileptic transmit to a part of their off- 
spring the disposition to various diseases of the nerves, to dis- 
eases of the motor nerves, and in a less degree to those of sensory 
nerves, and most markedly to those of trophic nerves. In rare 
instances, those in which paralysis is most developed in the off- 
spring, the epilepsy is also transmitted with it. 
If the pathological change in the nervous structures which 
follows injury and produces the epilepsy be due, as is possible, 
to some as yet unknown microbe growing within its substance, 
it is far easier to understand the transmi sion of such a microbe 
from the parent to the offspring in the adult sperm-cell or oyi- 
cell than to conceive of the disease being communicated in the — 
form of a molecular change in the germ-cell. That such a trans- 
ference of a microbe in the ovi-cell or sperm-cell occurs in the 
case of syphilis and tuberculosis is probable, and it is certain 
that such does occur in the case of the muscardine silkworm 
disease. Such an explanation would account, in the case of the 
guinea-pigs, for the fact that the various offspring exhibit various 
forms of nerve diseases, which remains unexplained if it be 
assumed that this is a case in which there is an hereditary trans- 
mission of a morphological character, namely, a pathological 
change of structure of a nervous centre. The way in which the — 
artificial epilepsy develops itself in the guinea-pigs after the 
operation, creeping gradually over the body, and ensuing in the 
same way after injury to the most varied parts of the nervous 
organs, is a proof of its infectious nature. he change produced 
by section of the nerves is obviously not the direct cause of the 
epilepsy, but only serves to originate a process of disease which 
is propagated centripetally, with the final result of the appear- 
ance of epileptic symptoms. ‘ 
The germ-plasma is immensely complex in its finest structure, 
but it has a remarkable power of persistence, since it absorbs 
nourishment and grows enormously without in the least changing 
its complicated molecular structure in so doing. This follows 
from the fact that many species (¢.g. the Igyptian ibis or the 
crocodile) have reproduced themselves for thousands of years 
without change. Further, since the quantity of germ-plasma 
contained in the single germ-cell must be regarded as extremely 
small, and as only a minute fraction of this remains unchanged 
when the germ-cell becomes developed into the new individual, — 
the growth of this fraction in the individual must be a most — 
enormous one, as usually thousands of germ-cells are produced , 
by it. : 
Gites the germ-plasma can remain unchanged in molecular 
structure in spite of such vast increase in bulk, it is obvious that — 
it is not easily to be modified, and it is probable that the direct 
influence of modifications in surrounding conditions on the germ- 
plasma has no effect of any importance on the production of 
hereditary individual variations. These must have another 
origin, and this, according to Weismann, is to be sought in the 
mode of reproduction occurring amongst most organisms at 
present existing—sexual, or as Haeckel terms it, amphigonic re- — 
production. ‘This consists, as is well known, in the fusion of 
two antithetic germ-cells, or possibly nuclei only, which con-_ 
tain the germ-plasma, which in virtue of its peculiar molecular — 
structure, is the bearer of the hereditable tendencies of the 
organism from which the germ-cell originates. Thus in amphi- 
gonic reproduction two diffe eat sets of hereditable tendencies — 
are to a certain extent mingled with one another. It is this — 
process of mingling which is the cause of the occurrence of — 
hereditarily transmissible individual peculiarities, and it is the 
production of these peculiarities which it is the office of amphi-— 
gonic reproduction to effect. Amphigonic reproduction supplies” 
the material for the development of individual variation out of 
which selection produces new species. pt 
This is a most startling conclusion, and directly opposed to 
almost all former views on the action of sexual reproduction, 
The amphigonic process has been regarded as having the effect 
of rapidly obliterating any deviations from the specific type 
which may arise in the members of a species. With regard to 
specific characteristics this may still hold true, since the devia- 
tions from them are of so rare occurrence that they are unable 
to hold their own against the great mass of normally-formed 
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