Juny 16, 1897.] 
his treatise into three parts, which he en- 
entitles: I. The Nature of Variation; II. 
The Causes of Variation; III. The Inher- 
itance of Variation. He begins the Part 
III. by saying that he proposes to cite ‘‘ ex- 
amples of the direct modifying effect of 
external influences on the character of in- 
dividual animals and plants. These influ- 
ences fall naturally into two classes, viz., 
the physico-chemical (molecular) and the 
mechanical (molar). The modifications so 
presented are supposed to be the result of 
the action of the causes in question, con- 
tinued throughout geological time’ (p. 
225). A few of the examples cited are the 
conversion of Artemia salina, a salt-water 
Crustacean into a Branchinecta, a genus 
accustomed to fresh-water habits; the pro- 
duction of colors in Lepidopterous pup; 
light and feeding affecting the color of fish ; 
the case of the blindness of cave animals ; 
Dr. Dall’s theory of the origin of plaits in the 
Gastropoda; the moulding the shape of the 
articulation of bones in accordance with the 
dominant strain put upon them; the mechan- 
ical origin of dental types in Vertebrates. 
No question is here raised as to the real- 
ity of the observed phegomena; the associa- 
tion of particular modifications of organic 
structure with change in the conditions of 
environment to which the organisms are 
subjected is not disputed. But the specific 
question raised is this: Does environment 
in general, or do the external influences of 
a chemico-physical or mechanical nature 
(to use Cope’s phrases), exert an influence 
over growing organisms to induce them 
to depart from the order of phenomena of 
their ancestors, or do these influences or 
forces produce the opposite effect of control- 
ling and limiting variation? From the quo- 
tations it will be evident that the theory is 
clearly expressed in the writing of the two 
prominent schools of evolution of to-day 
that these external influences do, either directly 
or indirectly, produce the variations. 
SCIENCE. 
at 
Several years ago my studies led me to 
doubt the validity of this view, and a care- 
ful study of the order of sequence shown in 
the succession of species in geological time 
has confirmed this opinion. My friend and 
former neighbor, Professor Bailey, of Cor- 
nell, a pupil and ardent disciple of Asa 
Gray, has been led to the same conclusion 
from the study of plants, and he has sup- 
ported and given botanical evidence for the 
validity of the theory in this book on ‘ The 
survival of the unlike’ (Macmillan, 1896, 
see p. 21, 22). I also presented some evi- 
dence of paleontological nature which seems 
to support the view (‘ Geological Biology,’ 
1894’). The present paper is intended to 
consider the philosophical line of reasoning 
upon which the theory rests. 
The commonly held conception seems to 
be that variation, and consequently the es- 
sential essence of evolution, is some kind of 
modification of ordinary generation. So 
much is this true that in most minds and 
in standard treatises on evolution the two 
words development and evolution are used 
as Synonymous terms. 
We may then resolve the question into 
this concrete form: In the case of any par- 
ticular organic cycles of phenomena, is it 
more simple and fundamental for the organ- 
ism to reproduce its kind or to produce 
itself, i. e., its mature self from the germ? 
We can logically find but one reply to this 
question. Production must precede repro- 
duction. But what does this answer imply? 
It implies that the processes of development 
of the individual from the germ to the adult 
do, in their intrinsic nature, precede the 
phenomena of reproduction. It further im- 
plies that the phenomena of evolutional 
variation are supplementary to, and then a 
further pushing on of, the phenomena of in- 
dividual development. The assumption, 
which is generally accepted, appears to be 
that this mode of variation is a modification 
of ordinary reproduction, either produced 
