be very nearly that of the hand to the iron filings that follow,
canalize and limit its motion.

The greater the effort of the hand, the farther it will go into the
filings. But at whatever point it stops, instantaneously and
automatically the filings coordinate and find their equilibrium. So with
vision and its organ. According as the undivided act constituting vision
advances more or less, the materiality of the organ is made of a more or
less considerable number of mutually coordinated elements, but the order
is necessarily complete and perfect. It could not be partial, because,
once again, the real process which gives rise to it has no parts. That
is what neither mechanism nor finalism takes into account, and it is
what we also fail to consider when we wonder at the marvelous structure
of an instrument such as the eye. At the bottom of our wondering is
always this idea, that it would have been possible for _a part only_ of
this coordination to have been realized, that the complete realization
is a kind of special favor. This favor the finalists consider as
dispensed to them all at once, by the final cause; the mechanists claim
to obtain it little by little, by the effect of natural selection; but
both see something positive in this coordination, and consequently
something fractionable in its cause,--something which admits of every
possible degree of achievement. In reality, the cause, though more or
less intense, cannot produce its effect except in one piece, and
completely finished. According as it goes further and further in the
direction of vision, it gives the simple pigmentary masses of a lower
organism, or the rudimentary eye of a Serpula, or the slightly
differentiated eye of the Alciope, or the marvelously perfected eye of
the bird; but all these organs, unequal as is their complexity,
necessarily present an equal coordination. For this reason, no matter
how distant two animal species may be from each other, if the progress
toward vision has gone equally far in both, there is the same visual
organ in each case, for the form of the organ only expresses the degree
in which the exercise of the function has been obtained.

But, in speaking of a progress toward vision, are we not coming back to
the old notion of finality? It would be so, undoubtedly, if this
progress required the conscious or unconscious idea of an end to be
attained. But it is really effected in virtue of the original impetus of
life; it is im