50 
NATURE 
[Mov. 17, 1870 


those leading to new genera and families, because the 
changes effected are wholly superficial and are almost 
entirely confined to colour. Now colour is both more 
variable than any other character, and is less intimately 
correlated with structure, so that great changes of colour 
may rapidly occur without in any other way affecting the 
individual, as we see in almost all our domestic animals, 
Experiments in breeding show that very large spontaneous 
variations of colour are frequent in insects ; and thus the 
number of steps to produce a required amount of change 
may be much fewer than in cases of structural modification, 
in which every other part of the organism has to be co- 
ordinated to work harmoniously with the modified organ. 
I may here take the opportunity of denying that I have 
argued, as Mr. Bennett says I have, that “an infi- 
nilesimal and inappreciable distinction may make the 
difference of a slightly longer span of life being allowed 
to the butterfly to lay its eggs in safety ;” and I cannot 
imagine how he could have imputed to me anything so 
absurd. What I have maintained is, that for natural selec- 
tion to act, either in producing “ mimicry,” or structural 
changes, no large or special variations are required, 
because the usual amount of variability which occurs in 
every part of every organism is sufficient. (‘‘ Contribu- 
tions,” pp. 287—291.) but so far from supposing this to 
be “ infinitesimal” or “ inappreciable,” I show that it is so 
palpable and so readily appreciated by horticulturists and 
breeders as to have enabled them to produce all the 
wonderful variety in our domestic animals and cultivated 
plants. And every entomologist knows that similar vari- 
ability exists in insects, and that the constantly occurring 
variations of colour are especially great. 
Mr. Bennett next returns to the laws of variation, and, 
because Mr, Darwin says that we are profoundly ignorant 
of these (although he himself has done so mucb to eiuci- 
date them), maintains that we cannot really know any- 
thing of the origin of species. As well might it be said 
that, because we are ignorant of the laws by which metals 
are produced and trees developed, we cannot know any- 
thing of the origin of steamships and railways. Sponta- 
neous “variations” are but the materials out of which 
“species” areiormed, and we donot require to know how 
the former are produced in order to learn the origin of 
the latter. But though we may not know the laws which 
determine each variation in detail, the general causes 
which lead to variation are not dithcult to perceive. We 
do not know all the laws and causes that have given their 
peculiar form to each mountain or each valley, but we 
know a good deal of the general causes which have pro- 
duced them, and we can perceive that the reason no two 
are exactly alike is, the number and complexity of the 
causes and the endless variety of conditions under which 
these causes have acted, In the far more complex opera- 
tions of the development and growth of organisms, affected 
as we know they are by almost infinitely numerous and 
ever varying external and internal causes, it would bea 
much greater mystery if there were no variations, and if 
absolut ly identical forms were produced by constant 
diversity of condiiions. Even the successive offspring of 
the same parents are developed under very different condi- 
tions. At each succeeding year, and at every different 
period of each year, the parents have changed in age, in 
size, in vigour, health, and constitution; they may be 
living in a different locality, have different food, and be 
subjected to very different physical and mental influences. 
Add to this the effect of cross unions of distinct 
individuals, each with its own characteristic pecu- 
liarities, which are in varying degrees transmitted 
to the offspring; and further, that these modified 
offspring are submitted to a somewhat different set of 
conditions from the parents, and intercross perhaps with 
a distinct set of individuals ; and then add the effects of 
atavism in bringing up long lost ancestral characters, and 
it can hardly be said that the almost universal fact of 

“ spontaneous variation” is quite unaccounted for. But, 
as I have already remarked, this variability could never by 
itself produce sfecies, but must absolutely prevent their 
production without the eliminating, accumulating, and 
fixing powers of selection, multiplication, and heredity. 
In Mr. Bennett’s concluding passages he advances a 
theory of his own on the subject of “mimicry,” to the 
effect that it is connected with intelligence or instinct, 
“and runs almost farz passu with the development of the 
nervous system.” In support of this view he asserts that 
it is “strongly developed in birds.” This is erroneous. 
In birds it is very rare, only two or three cases being 
known, and these not nearly so remarkable as hundreds 
that occur in insects ; and in mammalia, with the excep- 
tion of one doubtful case, it is absolutely unknown. 
This view, therefore, is directly opposed by the facts. 
I have only one more point to notice, a charge of incon- 
sistency against myself. Mr. Bennett quctes me to the 
effect that man’s chief peculiarities of form and structure 
were developed before his intellect had raised him above 
the condition of the brutes, and also zwzfputes to me the 
belief that certain peculiarities in his structure (the ab- 
sence of hair on his body, for example) “ must have been 
in some way connected with /zs reasoning powers.” But 
this is Dr. Laycock’s view, which I have expressly repu- 
diated, and I have never used a word to show that I 
believed that man has modified his own structure in any 
important degree, by the conscious or unconscious exercise 
of his reasoning powers. 1 have, it is true, declared my 
belief that “some intelligence” has acted on him, but I 
have also, I think, made it quite clear thet I did not be- 
lieve it to be his own intelligence. The inconsistency, 
therefore, is of Mr. Bennett’s making. 
I think I have now noticed the chief points in this last 
assault on the theory of Natural Selection, which has 
failed, like all preceding ones. Its author also exhibits 
the usual inability to keep steadily before him the great 
fundamental principles of the theory he is discussing, so 
that his arguments continually break down owing to his 
taking a partial and wholly inadequate view of its mode 
of operation. In the case of “mimicry” he is not suffi- 
ciently careful in his statement of the facts, and this, com- 
bined with his imperfect grasp of the theory, entirely 
neutralises the elaborate numerical proofs which at first 
sight appear so overwhelming. ALFRED R. WALLACE 
SCIENCE IN PARIS 
[X the course of an article on the present condition of 
Paris, the Engineer gives the following account of 
the effects of the war. The use of the electric light is 
common to both sides in the present struggle, but the 
French have used it largely. The apparatus set up on 
Montmartre is arranged by M. Bazin, and is electro- 
magnetic. The central cylinder supports four series of 
double coils covered with copper wire enveloped in silk ; 
the cylinder is rotated by a small steam-engine of 3-horse 
power, making 400 revolu'ions per minute. The lamp 
used is of the ordinary form, with the Foucault-Dubose 
regulator. The reflector is parabolic in form, and the 
whole is surrounded by a shield to hide it from the enemy. 
This light, from its elevated position, commands the 
whole of Paris and the plains around. A spectator on 
Montmartre sees distinctly the details of the facade of a 
building which stands 2,600 metres off ; at 2,900 metres 
aman may be seen standing at a window, at 3,000 metres 
amass of cavalry or infantry is distinguishable, and at 
4,000 metres the dome of the Invalides, with its bands of 
gold, is brilliant. A man cannot be seen on the dome at 
that distance, but on walking towards the building all 
soon becomes clear. On the ramparts, at 3,800 metres 
from Montmartre, the light is sufficient to read an ordinary 
newspaper. = 
a 


