inged Insects, with head, chest, and hind body distinct from each
other, forming three separate regions. In the first group, the
Centipedes, the nervous system is scattered through the whole body, as
in the Worms; in the Spiders it is concentrated in two nervous
swellings, as in the Crustacea, the front one being the largest; and in
the Insects there are three nervous centres, the largest in the head, a
smaller one in the chest, and the smallest in the hind body. Now
according to this greater or less individualization of parts, with the
corresponding localization of the nervous centres, naturalists have
established the relative rank of these three groups, placing Centipedes
lowest, Spiders next, and Winged Insects highest. But naturalists may,
and indeed they actually do, differ as to this estimation of the
anatomical structure. Have we, then, any means of testing its truth to
Nature? Let us look at the development of these animals, taking the
highest order as an illustration, that we may have the whole succession
of changes. All know the story of the Butterfly with its three lives, as
Caterpillar, Chrysalis, and Winged Insect. I speak of its three lives,
but we must not forget that they make after all but one life, and that
the Caterpillar is as truly the same being with the future Butterfly as
the child is the same being with the future man. The old significance of
the word _metamorphosis_--the fabled transformation of one
individual into another, in which so much of the imagination and
poetical culture of the ancients found expression--still clings to us;
and where the different phases of the same life assume such different
external forms, we are apt to overlook the fact that it is one single
continuous life. To a naturalist, metamorphosis is simply growth; and in
that sense the different stages of development in animals that undergo
their successive changes within the egg are as much metamorphoses as the
successive phases of life in those animals that complete their
development after they are hatched.

But to return to our Butterfly. In its most imperfect, earliest
condition, it is Worm-like, the body consisting of thirteen uniform
rings; but when it has completed this stage of its existence, it passes
into the Chrysalis state, during which the body has two regions, the
front rings being soldered together to form the head and chest, while
the hind joints remain distinct; and it is only when it bursts from its
Chrysa