Wilson has good reason for his “steadily growing conviction that the cell is not a self-regulating mechanism in itself, that no cell is isolated, and that Weismann’s fundamental proposition is false.”

But, granting the force of these criticisms, the question still remains, Is the special effect of use or disuse transmissible?  Would the blacksmith’s son have a stronger right arm?

1.  The isolation and independence of the germ-cells, which Weismann postulates as opposing this, can hardly be as great as he thinks. 2.  It is in his view impossible to conceive how these acquired characteristics can in any way reach and affect the germ-cells in such a manner as to reappear in the next generation. 3.  All variations can be explained by his own theory without such transmission.  Why then believe that acquired characteristics can in some inconceivable way affect the germ-cells so as to reappear in the next generation, as long as all the facts can be explained in a more simple and easily conceivable manner?

As to his second argument, I would readily acknowledge that it is at present difficult or impossible for me to conceive how any cell can act upon another, except through the nutrient or other fluids which it can produce.  But though I cannot conceive how one cell can affect another, I may be compelled to believe that it does so.  And this Weismann readily acknowledges.

Driesch changed by pressure the relative position of the cells of a very young embryo, so that those which in a normal embryo would have produced one organ were now compelled, if used at all, to form quite a different one.  And yet these displaced cells formed the organ required of cells normally occupying this new position, not the one for which they were normally intended.  And the organ which they would have builded in a normal embryo was now formed by other cells transferred to their rightful place.

What made them thus change?  Not change of substance or structure, for the slight pressure could hardly have modified this.  Not change of nutriment.  The only visible or easily conceivable change was in position relative to other cells of the embryo.

Let us in imagination simplify Driesch’s experiment, for the sake of gaining a clearer view of its meaning.  In a certain embryo at an early stage are certain cells whose descendants should form the lining of the intestine and be used in the adult for digestion.  A second set of cells should form muscle endowed mainly with contractility.  When these two sets of cells, or some of them, exchange positions in the embryo, they exchange lines of development.  The first set now form muscle, the second digestive tissue.  The only change has been in their relative positions.  Driesch maintains, therefore, that the goal of development in any embryonic cell is determined not by structure or nutriment but by position.  And this would seem to be true of the cells of the earliest embryonic stages.