legs and antennae become
rudimentary, and they feed on honey; so that they now more closely
resemble the ordinary larvae of insects; ultimately they undergo a
further transformation, and finally emerge as the perfect beetle. Now,
if an insect, undergoing transformations like those of the Sitaris, were
to become the progenitor of a whole new class of insects, the course of
development of the new class would be widely different from that of
our existing insects; and the first larval stage certainly would not
represent the former condition of any adult and ancient form.

On the other hand it is highly probable that with many animals the
embryonic or larval stages show us, more or less completely, the
condition of the progenitor of the whole group in its adult state. In
the great class of the Crustacea, forms wonderfully distinct from each
other, namely, suctorial parasites, cirripedes, entomostraca, and even
the malacostraca, appear at first as larvae under the nauplius-form; and
as these larvae live and feed in the open sea, and are not adapted for
any peculiar habits of life, and from other reasons assigned by Fritz
Muller, it is probable that at some very remote period an independent
adult animal, resembling the Nauplius, existed, and subsequently
produced, along several divergent lines of descent, the above-named
great Crustacean groups. So again, it is probable, from what we know of
the embryos of mammals, birds, fishes and reptiles, that these animals
are the modified descendants of some ancient progenitor, which was
furnished in its adult state with branchiae, a swim-bladder, four
fin-like limbs, and a long tail, all fitted for an aquatic life.

As all the organic beings, extinct and recent, which have ever lived,
can be arranged within a few great classes; and as all within each
class have, according to our theory, been connected together by fine
gradations, the best, and, if our collections were nearly perfect, the
only possible arrangement, would be genealogical; descent being the
hidden bond of connexion which naturalists have been seeking under the
term of the Natural System. On this view we can understand how it is
that, in the eyes of most naturalists, the structure of the embryo is
even more important for classification than that of the adult. In two or
more groups of animals, however much they may differ from each other
in structure and habits in their adult condition, if they pass through
closely similar