i. With a corneous head of determinate shape (coleopterous and

hymenopterous _apods_--_Culicidæ_, some _Tipulidæ_, &c. amongst the _Diptera_).

ii. With a membranaceous head of indeterminate shape (_Muscidæ_, _Syrphidæ_, and other _Diptera_).

II. Larvæ with legs.