e
liable to have their undulations affected by every external force, and,
once modified, the movement does not return to its pristine condition.
By assimilation they continually increase to a certain point in size,
and then divide, and thus perpetuate in the undulatory movement of
successive generations, the impressions or resultants due to the action
of external agencies on individual plastidules. This is Memory. All
plastidules possess memory; and Memory which we see in its ultimate
analysis is identical with reproduction, is the distinguishing feature
of the plastidule; is that which it alone of all molecules possesses, in
addition to the ordinary properties of the physicist's molecule; is, in
fact, that which distinguishes it as vital. To the sensitiveness of the
movement of plastidules is due Variability--to their unconscious Memory
the power of Hereditary Transmission. As we know them to-day they may
'have learnt little, and forgotten nothing' in one organism, and 'have
learnt much, and forgotten much' in another; but in all, their memory if
sometimes fragmentary, yet reaches back to the dawn of life upon the
earth.--E. Ray Lankester."

Nothing can well be plainer and more uncompromising than the above.
Professor Hering would, I gather, no less than myself, refer the
building of its nest by a bird to the intense--but unconscious, owing to
its very perfection and intensity--recollection by the bird of the nests
it built when it was in the persons of its ancestors; this memory would
begin to stimulate action when the surrounding associations, such as
temperature, state of vegetation, &c., reminded it of the time when it
had been in the habit of beginning to build in countless past
generations. Dr. Darwin does not go so far as this. He says that wild
birds choose spring as their building time "from their _acquired_
knowledge that the mild temperature of the air is more convenient for
hatching their eggs," and a little lower down he speaks of the fact that
graminivorous animals generally produce their young in spring, as "part
of the traditional knowledge which they learn _from the example_ of
their parents."[156]

Again he says, that birds "seem to be instructed how to build their
nests _from their observation_ of that in which they were educated, and
from their knowledge of those things that are most agreeable to their
touch in respect to warmth, cleanliness, and stability."

Had Dr. Darwin laid firmly hold of tw