540 The American Naturalist. [Jaly, 
resulting in abnormal development, and there are some very © 
interesting experiments which I shall cite on this point; from 
some nervous disorders which profoundly modify cell-function 
in all the tissues; in other words, ovum sanum in corpore sano. 
But to accept all this, and even to include all our rapidly 
increasing knowledge of the direct relation between such phe- 
nomena as production of deformities and determination of 
sex, and the influences of environment upon the ovum; or 
the influences of the mother upon the foetus—this is all aside 
from the real question at issue. 
It may be stated thus: Given G, the ova and spermatozoa, 
the germ-cells or material vehicles of hereditary characters; 
S, the body of somatic cells of all the other tissues conveying 
the hereditary characters of nerve, muscle, and bone; V, the 
variations in these body-cells “acquired” during lifetime; 
given these factors, the real question is: Do influences at work 
producing variations in certain body-cells of the parent so 
affect the germ-cells of the parent that they reappear in cor- 
responding body-cells of the offspring? To take a concrete case, 
will the increased use of the cells of the extensor indicis mus- 
cle in the parent so stimulate that portion of the germ-cells 
which represents this muscle that the increment of growth 
will in any degree reappear in the offspring? 
This is what is required of heredity upon the Lamarckian 
hypothesis, and I think you will see at once that while this 
hypothesis simplifies the problem of evolution it in a corres- 
ponding degree renders more difficult the problem of heredity 
—for we have not the first ray of knowledge of what such a 
process involves. There is no quality more essential to the 
scientific progress than common honesty; if we take a posi- 
tion let us face all its consequences; the more we reflect 
upon it, the more serious the Lamarckian position becomes. 
In the present lecture let us first briefly review the progress 
of the science of heredity which has led up to the present 
discussion. Second, Let us examine the evidence for and 
against the Lamarckian theory, and inquire how far natural 
selection can explain all the facts of evolution. Third, Let us 
examine the evidence for such a continuous relation between 
