Primarily wingless insects (very primitive with very little metamorphosis) containing 4 orders. When we say primarily wingless we mean that as far as we know these insects never had wings at any time in the past. Some insects which are now wingless are in the Pterygota  (winged) section because we believe they have evolved from insects which had wings in the past, we call this being secondarily wingless, fleas are an example of a secondarily wingless insect.