A Criticism of the Cell-Theory; being an Answer to Mr. Sedgwick's ...

A CRITICISM OF THE CELL-THEORY. 143
in Unio, there result from the division of the ovum separate
protoplasmic corpuscles, as distinct from one another as one
room in a house is distinct from another, each of which is not
only separate, but contains within itself definite, and probably
limited, qualities (at least at stages beyond eight or sixteen
cells). One might almost say that, after the earliest stages,
each blastomere has a definite task allotted to it, which it
faithfully and punctually performs, according to a prescribed
course. To each, it might be said in figurative language, isgiven
material, which it must place, not anywhere, but in one
particular part of the edifice.
In considering these very remarkable researches, it is not
sufficient, for the present purpose, to say that no connection
between the blastomeres was observed. Such connections
may have existed and have been overlooked; as the connections,
which undoubtedly exist, between plant cells were
for a long time overlooked. But, a priori, such connections
are improbable. For, as has been said, the qualities of each
blastomere are limited. Each is specialised before any form
changes become visible; each plays one part, and one part
Only in tissue formation. If their protoplasm were continuous,
being made so by uniting strands, then, as Mr. Sedgwick has
expressed it, the molecular constitution of any part would in
time spread through the whole mass. But the molecular
constitution of the blastomeres must be different, for their
manifestations are different, and we may possibly see, in this
case, some explanation, obscure though it may be, of the isolation
of the form elements from one another.
Further than this, there is objective proof that the cells
constituting the early embryos of these forms are separate.
They exhibit remarkable shiftings of position, which render
the existence of connecting strands of protoplasm highly improbable,
and the migrations of some cells—e. g. those in
Nereis named c 1>5< and d 1>6> by Wilson—are of such an extent
that, if there were protoplasmic continuity, they would be
impossible.
It is no exaggeration to say that this is evidence which-