Most significant is the precedence of the eruciform by the campodeiform type.
Larva campodeiform, usually feeding by suction (exceptionally hypermetamorphic with subsequent eruciform instars).
Larvae eruciform, with rarely more than five pairs of abdominal prolegs.
Larvae eruciform without thoracic legs, or vermiform without head-capsule.
Larva eruciform, limbless.
Larva eruciform, with seven or eight pairs of abdominal prolegs, or entirely legless.
The occurrence in the hypermetamorphic Coleoptera (see supra) of a campodeiform preceding an eruciform stage in the life-history is most suggestive.
The antiquity of the Coleoptera is further shown by the great diversity of larval form and habit that has arisen in the order, and the proof afforded by the hypermetamorphic beetles that the campodeiform preceded the eruciform larva has already been emphasized.
In all the remaining orders of the Endopterygota the larva is eruciform or vermiform.
The eruciform larva of the Orthorrhapha leads on to the headless vermiform maggot of the Cyclorrhapha, and in the latter sub-order we find metamorphosis carried to its extreme point, the muscid flies being the most highly specialized of all the Hexapoda as regards structure, while their maggots are the most degraded of all insect larvae.