280 
NATURE 
[ Fan. 18, 1883 
attempts at classifications deduced from the developmental stages 
of eggs and larvz of questionable origin, and applied to groups 
of animals of which the adventurous embryologist would cer- 
tainly not be able to distinguish the different members speci- 
fically. 
But enough of this distressing partiality, knowing that we 
find a complete reaction against it, in Darwin’s word and ex- 
ample, which will be our strongest antidote against similar in- 
fluences. We are thus carried back to our starting-point, where 
it was observed that the value of the sources from whence Darwin 
has drawn so much valuable information, was scarcely recognised 
up to his time. He entered into connection with cattle-rearers 
and bird-fanciers, and gladly availed himself of the remarks of 
trustworthy observers who were acquainted with animals and 
plants in their daily life, even if they had always remained out- 
side the pale of science. 
And what far-reaching results may be obtained by careful 
study of the habits and life-history of animals is shown by the 
last volume which we owe to Darwin’s hand, Here it is appa- 
rent, upon almost every page, that from conscientious observa- 
tions on the habits of an animal so common as the earthworm, 
conclusions follow which furnish us with new and quite unex- 
pected views about the formation and the changes of a large area 
of the earth’s surface. 
The most striking example of Darwin's all-embracing genius 
is obtained when his Monograph of the Cirripedia is compared 
with the chapters in which he enunciates and discusses his 
hypothesis of pangenesis. The one, the most scrupulous study 
of details, the comparison of slight differences both between 
individuals of the same species and between specifically distinct 
specimens; the evaluation of these distinctive characters one 
against the other ; in one word, pure systematic zoology with all 
its appurtenance of patience, scrupulousness, and nearly painful 
conscientiousness. The other—one of the most daring hypo- 
theses which the human understanding has ever wrought, upon 
which only a yery limited number cf observed facts can be 
brought to bear. A hypothesis which boldly penetrates into the 
most hidden secrets of organic nature ; which brings the mar- 
vellous effects of heredity on a level with the reproduction of 
lost parts, yea even with the healing of wounds, A hypothesis 
which no longer looks upon the cells as the morphological units 
of the living organism, but which postulates the existence of a 
continual flow of separate minute gemmulz, feeding and repro- 
ducing themselves, and being derived from all the cells and all 
the tissues in all the consecutive periods of their existence. 
These gemmulz, in the individual being we have before us, cir- 
culate along paths which remain wholly unknown to us, and 
finally reunite in millions in every ovum, in every spermatozoon, 
in every bud, and in every pollen-grain. 
The laws by which these inscrutinable processes are governed, 
do not lose anything of their mysteriousness when we glance at 
the disparate and incomprehensible phenomena which they have 
to explain: atavism, in which heredity takes a sudden leap 
backwards into the grey mists of the past; the transmission to 
the child of the effects of an increased or decreased use of a 
limb by the parents: the reproduction of a lost limb or tail; the 
growth of an entire plant out of a severed portion of a leaf; 
the change which pollen and sperma may occasionally call forth 
not only in the ovules but also in the tissues of the mother-form ; 
the hybridisation in the vegetable kingdom by the union of the 
cellular tissue of two plants independently of the organs of 
generation ; the appearance of a complex metamorphosis in the 
course of the development of certain animal forms, the nearest 
allies of which are entirely devoid of anything like it; &c. 
Nevertheless this hypothesis was put forward by the very same 
Darwin whom we have to thank for the monograph of the Cirri- 
pedia. It is clear that the frame of mind required for completing 
the one is widely different from that in which he enunciated 
the other, There is, however, a common link uniting the two. 
In the specific description of the Cirripeds we find him ever and 
again in collision with the opinion then generally accepted of 
the definite boundaries limiting the species, and thus this work 
cannot have remained without influence on the later development 
of his ideas. On the other hand, he looked upon the hypothesis 
of pangenesis as a necessary sequel, to a certain extent as ‘‘le 
couronnement de l’edifice’”” of his theory of evolution by means 
of natural selection. 
We have not here to enter into a discussion concerning the 
hypothesis of pangenesis, nor to inquire into the different attacks 
to which it has already been exposed. I must, however, observe 
that with it Darwin has entered the domain of physiology, a 
field upon which all the questions into which the great problem 
of evolution may be subdivided, as heredity, influence of uce 
and disuse of organs, adaptation to modified circumstances, 
must find their solution, 
Whereas the physiology of man and the higher animals is 
developing and growing with rapidity, and what has been 
thought and wrought in Utrecht has largely influenced this 
development, Comparative Phy-iology, which has to track all the 
different problems just mentioned all through the animal king- 
dom down to their simplest form in the lowest organised beings, 
is only in its infancy. And yet this branch of science will shortly 
come abreast of morphology further to secure the basis of the 
theory of evolution and to contribute to its harmonious develop- 
ment. It was not by mere chance that the legislature specially 
mentions Comparative Physiology as a branch of science which 
will have to be cultivated and taught by him who is called to 
the chair I am about to occupy. 
Although the greater part of this territory is still wrapt in 
obscurity, still it is at the University of Utrecht that the pros- 
pects for Comparative Physiology are promising in the highest 
degree, be it by the efforts of others than the legislature had 
in view. It must for certain be acknowledged that researches 
concerning the phenomena of life in the very smallest organisms, 
investigating their reaction towards light and oxygen, and even 
penetrating into the effects of hunger and thirst as manifested 
by these lowly-organised beings, eminently belong to the domain 
of Comparative Phy-iology. The vicinity of a laboratory in 
which such excellent results have already been obtained is a 
strong stimulus for us all towards further labour in this field. 
Venturing to-day along that road, I may hope to claim your 
attention, because in so doing, I wish to make an attempt to 
weaken one of the chief arguments against the theory of evolu- 
tion, an argument which was termed by Huxley ‘*the stock 
objection.” 2 
I wish to speak to you about the hypothesis of accelerated 
development by primogeniture and its place in the theory of 
evolution. 
I must begin with calling to mind that provisionally it is not 
upon the firm basis of proved facts, but more upon the quick- 
sands of theoretical conjecture that we shall be moving. Our 
track first leads us into the domain of a science which is of such 
an exceptional value for the theory of evolution, because this 
science only, the science of palzontology, can furnish us wish 
direct evidence towards the truth of that theory. 
If, indeed, living organisms form one continuous chain with 
those that have already become extinct ; if these organisms have 
not been called into life in successive periods by repeated crea- 
tive acts but if they are in direct blood-relationship to each 
other—a relation which as we penetrate further into the past 
must be accompanied by a simplification of organisation—then 
paleontology must furnish us with the evidence of this pro- 
cess. Then, indeed, the superposed strata which have been 
deposited since the cooling of the earth’s crust under the com- 
bined influence of internal vulcanism and external atmospherical 
influences, must contain the archives in which the most trust- 
worthy and direct proof for the validity of the theory of evolu- 
tion are to be found. Moreover, the material which we find 
heaped in these archives must show—if we place confidence 
in it—that gradual increase of complication which accompanies 
the development of the more highly differentiated forms out of 
simpler types by the aid of natural selection, in a succession 
exactly corresponding to that of the deposition of the strata. We 
know how far palzeontology had advanced in 1859, we under- 
stand how it was that Darwin insisted on the imperfection of the 
geological record in the first edition of his ** Origin of Species.” 
He diligently collected arguments to explain this incompleteness 
and to oppose the objection against his doctrines which it might 
furnish, ~ I cannot at present enter into details concerning this 
refutation. Still it is quite as valid to-day. So many deposits 
are wholly devoid of animal remains, it is so obvious that of 
other animal forms, fossils can hardly ever have been formed, 
and lastly, only such a small portion of the earth’s surface has 
been adequately searched, that we have indeed more reason to be 
astonished at the quantity of facts that have already come to our 
knowledge, than at the much larger quantity which yet remains 
hidden from our view. : 
This is especially present to our minds when we remember 
* T. H. Huxley, American Addresses. 
