ch have the most
important bearing on evolution:--

"The ingenious Dr. Hartley, in his work on man, and some other
philosophers have been of opinion, that our immortal part acquires
during this life certain habits of action or of sentiment which become
for ever indissoluble, continuing after death in a future state of
existence; and add that if these habits are of the malevolent kind, they
must render their possessor miserable even in Heaven. I would apply this
ingenious idea to the generation or production of the embryon or new
animal, which partakes so much of the form and propensities of its
parent.

"_Owing to the imperfection of language the offspring is termed a new
animal, but is in truth a branch or elongation of the parent, since a
part of the embryon-animal is, or was, a part of the parent, and
therefore in strict language, cannot be said to be entirely new at the
time of its production; and, therefore, it may retain some of the habits
of the parent system._

"At the earliest period of its existence the embryon would seem to
consist of a living filament with certain capabilities of irritation,
sensation, volition, and association, and also with some acquired
habits or propensities peculiar to the parents; the former of these are
in common with other animals; the latter seem to distinguish or produce
the kind of animal, whether man or quadruped, with the similarity of
feature or form to the parent."[169]

* * * * *

Going on to describe the gradual development of the embryo, Dr. Darwin
continues:--

"As the want of this oxygenation of the blood is perpetual (as appears
from the incessant necessity of breathing by lungs or gills), the
vessels become extended by the efforts of pain or desire to seek this
necessary object of oxygenation, and to remove the disagreeable
sensations which this want occasions."[170]

. . . . . .

"The lateral production of plants by wires, while each new plant is thus
chained to its parent, and continues to put forth another and another as
the wire creeps onward on the ground, is exactly resembled by the
tape-worm or taenia, so often found in the bowels, stretching itself in a
chain quite from the stomach to the rectum. Linnaeus asserts 'that it
grows old at one extremity, while it continues to generate younger ones
at the other, proceeding _ad infinitum_ like a sort of grass; the
separate joints are called gourd worms, and propagate new joints like