s to provide for itself. The period
of activity may come on earlier or later in life; but whenever it comes
on, the adaptation of the larva to its conditions of life is just as
perfect and as beautiful as in the adult animal. In how important a
manner this has acted, has recently been well shown by Sir J. Lubbock
in his remarks on the close similarity of the larvae of some insects
belonging to very different orders, and on the dissimilarity of the
larvae of other insects within the same order, according to their habits
of life. Owing to such adaptations the similarity of the larvae of
allied animals is sometimes greatly obscured; especially when there is
a division of labour during the different stages of development, as
when the same larva has during one stage to search for food, and during
another stage has to search for a place of attachment. Cases can even be
given of the larvae of allied species, or groups of species, differing
more from each other than do the adults. In most cases, however, the
larvae, though active, still obey, more or less closely, the law of
common embryonic resemblance. Cirripedes afford a good instance of
this: even the illustrious Cuvier did not perceive that a barnacle was
a crustacean: but a glance at the larva shows this in an unmistakable
manner. So again the two main divisions of cirripedes, the pedunculated
and sessile, though differing widely in external appearance, have larvae
in all their stages barely distinguishable.

The embryo in the course of development generally rises in organisation.
I use this expression, though I am aware that it is hardly possible to
define clearly what is meant by organisation being higher or lower.
But no one probably will dispute that the butterfly is higher than
the caterpillar. In some cases, however, the mature animal must be
considered as lower in the scale than the larva, as with certain
parasitic crustaceans. To refer once again to cirripedes: the larvae in
the first stage have three pairs of locomotive organs, a simple single
eye, and a probosciformed mouth, with which they feed largely, for they
increase much in size. In the second stage, answering to the chrysalis
stage of butterflies, they have six pairs of beautifully constructed
natatory legs, a pair of magnificent compound eyes, and extremely
complex antennae; but they have a closed and imperfect mouth, and
cannot feed: their function at this stage is, to search out by their
well-developed