ffects the germinal matter in the sexual elements as much as it
does that in his own structural cells, which have led to an alteration
in the quality of his own nerves. Exactly the same must occur in the
case of many constitutional diseases that have been acquired by
long-continued irregular habits."[13]

INDIVIDUAL AND TRANSMISSIBLE TYPE NOT MODIFIED ALIKE BY THE DIRECT
EFFECT OF CHANGED HABITS OR CONDITIONS.

Mr. Spencer finds it hard to believe that the modifications conveyed to
offspring are not identical in tendency with the changes effected in the
parent by altered use or habit (pp. 23-25, 34). But it is perfectly
certain that the two sets of effects do not necessarily correspond. The
effect of changed habits or conditions on the individual is often very
far from coinciding with the effects on the reproductive elements or
the transmissible type. The reproductive system is "extremely
sensitive" to very slight changes, and is often powerfully affected by
circumstances which otherwise have little effect on the individual
(_Origin of Species_, p. 7). Various animals and plants become sterile
when domesticated or supplied with too much nourishment. The native
Tasmanians have already become extinct from sterility caused by greatly
changed diet and habits. If, as Mr. Spencer teaches, continued culture
and brain-work will in time produce lessened fertility or comparative
sterility, we may yet have to be careful that intellectual development
does not become a species of suicide, and that the culture of the race
does not mean its extinction--or at least the extinction of those most
susceptible of culture.

The reproductive elements are also disturbed and modified in innumerable
minor ways. Changed conditions or habits tend to produce a general
"plasticity" of type, the "indefinite variability" thus caused being
apparently irrelevant to the change, if any, in the individual.[14] A
vast number of variations of structure have certainly arisen
independently of similar parental modification as the preliminary.
Whatever first caused these "spontaneous" congenital variations affected
the reproductive elements quite differently from the individual. "When a
new peculiarity first appears we can never predict whether it will be
inherited." Many varieties of plants only keep true from shoots, and not
from seed, which is by no means acted on in the same way as the
individual plant. Seeing that such plants have _two_ reproductive
ty