Differences in the larva might, also,
become correlated with successive stages of its development; so that the
larva, in the first stage, might come to differ greatly from the larva in
the second stage, as is the case with many animals. The adult might also
become fitted for sites or habits, in which organs of locomotion or of the
senses, etc., would be useless; and in this case the metamorphosis would be
retrograde.
>From the remarks just made we can see how by changes of structure in the
young, in conformity with changed habits of life, together with inheritance
at corresponding ages, animals might come to pass through stages of
development, perfectly distinct from the primordial condition of their
adult progenitors. Most of our best authorities are now convinced that the
various larval and pupal stages of insects have thus been acquired through
adaptation, and not through inheritance from some ancient form. The
curious case of Sitaris--a beetle which passes through certain unusual
stages of development--will illustrate how this might occur. The first
larval form is described by M. Fabre, as an active, minute insect,
furnished with six legs, two long antennae, and four eyes. These larvae
are hatched in the nests of bees; and when the male bees emerge from their
burrows, in the spring, which they do before the females, the larvae spring
on them, and afterwards crawl on to the females while paired with the
males.
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