JUNE 21, 1901.] 
it predicates the normal stability of organic 
series. * 
The configuration of a valley may de- 
termine the banks of a river which flows 
through it, but the valley does not cause 
* ‘* But let the external conditions of a country alter 
* * * the original inhabitants must cease to be as 
perfectly adapted to the changed conditions as they 
were originally * * * such changes of external con- 
ditions would, from their acting on the reproductive 
system, probably cause the organization of those beings 
which are most affected to become, as under domesti- 
cation, plastic. Now, can it be doubted, from the 
struggle each individual has to obtain subsistence, 
that any minute variation in structure, habits or in- 
stincts, adapting that individual better to the new 
conditions, would tell upon its vigor and health ?.* * * 
Each new variety or species, when formed, will gener- 
ally take the place of, and thus exterminate, its less 
well fitted parent. ‘This I believe to be the origin of 
the classification and affinities of organic beings at all 
times ; for organic beings always seem to branch and 
sub-branch like the limbs of a tree from a common 
trunk, the flourishing and diverging twigs destroying 
the less vigorous, the dead and lost branches rudely 
representing extinct genera and families.’ 
Quite as definitely did Wallace state the same 
proposition in controverting the somewhat more nar- 
towly static idea that the variations of species are 
limited, as it were, to fixed points beyond which they 
cannot go in nature, or to which they must return 
if differentiated from the wild type by artificial 
selection. 
“But * * * there is a general principle in nature 
which will cause many varieties to survive the parent 
species, and to give rise to successive variations de- 
parting further and further from the original type, and 
which also produces in domesticated animals the 
tendency of varieties to return to the parent form. 
* * * Granted, therefore, a ‘ tendency ’ to reproduce 
the original type of the species, still the variety must 
ever remain preponderant in numbers, and under ad- 
verse physical conditions again alone survive. But 
this new, improved, and populous race might itself, in 
course of time, give rise to new varieties, exhibiting 
several diverging modifications of form, any one of 
which, tending to increase the facilities for preserving 
existence, must, by the same general law, in their 
turn become predominant. Here, then, we have pro- 
gression and continued divergence deduced from the 
general laws which regulate the existence of animals 
in a state of nature, and from the undisputed fact that 
varieties do frequently occur.’’ 
SCIENCE. 
‘aly requiring special explanation. 
973 
the water to run down hill. In the absence 
of this property of water valleys would be 
quite powerless to ‘give rise’ to rivers. 
Similarly, it is true that environment in- 
fluences organic evolution ; it may acceler- 
ate or retard, deflect or even set absolute 
barriers to change, but these facts afford no 
reason for believing that selection repre- 
sents a biological force. The vital river, 
when unconfined, is in motion; change is 
a law of organic succession; evolution is a 
property of protoplasm. 
Some rivers have direct courses, deep 
channels and swift currents; the water 
reaches the sea without much loss of time ; 
with such streams is comparable the evolu- 
tion of the organic groups which an active 
selection has kept well within the lines of 
utility, whose functional organization is so 
perfect that a useless structure or an un- 
protective color is looked upon as an anom- 
There 
are, however, other rivers the waters of 
which give no suggestion of haste: they 
meet innumerable turns, eddies and back- 
sets, they are divided by islands, and often 
overflow the land. With such rivers may 
be compared the evolution of groups like the 
Diplopoda, not confined by too exact re- 
quirements of utility, and hence the better 
able to manifest the natural tendency to in- 
definite change. 
Darwin and Wallace recognized the fact 
that a species does not constitute a single 
morphological point, but that the projection 
of its characters requires a surface of ap- 
preciable area. And assuming that there 
is a tendency or law by which such an area 
remains even approximately constant in 
size, they found that it could be given a 
progressive motion by taking away from 
one side while permitting the other to grow 
out. Thus it appeared possible by pred- 
icating external causes to explain evolu- 
tionary progress with but a slight readjust- 
ment of the traditional static view of organic 
