f larval
and nymphal life, while the winged imago takes no food and devotes its
energies through its short existence to the task of reproduction. Such
division of the life-history into a long feeding, and a short breeding
period has, as will be seen later, an important bearing on the question
of insect transformation generally, and the dragon-flies and may-flies
afford examples of two stages in its specialisation. The sub-imaginal
instar of the may-fly furnishes also a noteworthy fact for comparison
with other insect histories. In two points, however, the life-story of
these flies with their aquatic larvae recalls that of the cockroach. All
the larval and nymphal instars are active, and the wing-rudiments are
outwardly visible long before the final moult.

CHAPTER V

TRANSFORMATIONS,--OUTWARD AND INWARD

We are now in a position to study in some detail the transformation of
those insects whose life-story corresponds more or less closely with
that of the butterfly, sketched in the opening pages of this little
book. In the case of some of the insects reviewed in the last three
chapters, the may-flies and cicads for example, a marked difference
between the larva and the imago has been noticed; in others, as the
coccids, we find a resting instar before the winged condition is
assumed, suggesting the pupal stage in the butterfly's life-story.

The various insect orders whose members exhibit no marked divergence
between larva and imago (the Orthoptera for example) are often said to
undergo no transformation, to be 'Ametabola.' Those with life-stories
such as the dragon-flies' are said to undergo partial transformation,
and are termed 'Hemimetabola.' Moths, caddis-flies, beetles, two-winged
flies, saw-flies, ants, wasps, bees, and the great majority of insects,
having the same type of life-story as the butterfly, are said to undergo
complete transformation and are classed as 'Metabola' or 'Holometabola.'
Wherein lies the fundamental difference between these Holometabola on
the one hand and the Hemimetabola and Ametabola on the other? It is not
that the larva differs from the imago or that there is a passive stage
in the life-history; these conditions are observable among insects with
a 'partial' transformation as we have seen, though the resting instar
that simulates the butterfly pupa is certainly exceptional. It has been
pointed out by Sharp (1899) that the most important indication of the
difference between the