produced for
ever. Yet opposite as are these curves in all their properties, they may
be connected together by a series of intermediate curves, no one of
which differs from the adjacent ones in any appreciable degree. Thus, if
a cone be cut by a plane at right angles to its axis we get a circle.
If, instead of being perfectly at right angles, the plane subtends with
the axis an angle of 89 deg. 59', we have an ellipse which no human eye,
even when aided by an accurate pair of compasses, can distinguish from a
circle. Decreasing the angle minute by minute, the ellipse becomes first
perceptibly eccentric, then manifestly so, and by and by acquires so
immensely elongated a form, as to bear no recognizable resemblance to a
circle. By continuing this process, the ellipse passes insensibly into a
parabola; and, ultimately, by still further diminishing the angle, into
an hyperbola. Now here we have four different species of curve--circle,
ellipse, parabola, and hyperbola--each having its peculiar properties
and its separate equation, and the first and last of which are quite
opposite in nature, connected together as members of one series, all
producible by a single process of insensible modification.

But the blindness of those who think it absurd to suppose that complex
organic forms may have arisen by successive modifications out of simple
ones, becomes astonishing when we remember that complex organic forms
are daily being thus produced. A tree differs from a seed immeasurably
in every respect--in bulk, in structure, in colour, in form, in chemical
composition: differs so greatly that no visible resemblance of any kind
can be pointed out between them. Yet is the one changed in the course of
a few years into the other: changed so gradually, that at no moment can
it be said--Now the seed ceases to be, and the tree exists. What can be
more widely contrasted than a newly-born child and the small,
semi-transparent spherule constituting the human ovum? The infant is so
complex in structure that a cyclopaedia is needed to describe its
constituent parts. The germinal vesicle is so simple that it may be
defined in a line. Nevertheless a few months suffice to develop the one
out of the other; and that, too, by a series of modifications so small,
that were the embryo examined at successive minutes, even a microscope
would with difficulty disclose any sensible changes. That the uneducated
and the ill-educated should think the hypothesi