Latreille to the primitive wingless insects known as springtails and bristletails.
Lubbock (Lord Avebury) separated the springtails as a distinct order, the Collembola, and by many students this separation has been maintained.
But the bristle-tails and springtails, which form the modern order Aptera, are all without any trace of wings, and, on account of several remarkable archaic characters which they exhibit, there is reason for believing that they are primitively wingless - that they represent an early offshoot which sprang from the ancestral stock of the Hexapoda before organs of flight had been acquired by the class.
Most springtails are without air-tubes, and breathe through the general cuticle of the body.
In many genera of springtails a curious post-antennal organ, consisting of sensory structures (often complex in form) surrounded by a firm ring, is to be noticed on the cuticle of the head between the eyes and the feelers.
The springtails have even a wider distribution.
Springtails and bristle-tails live in damp concealed places - under stones or tree-bark, in moss, and in the decaying vegetable or animal matter which serves as food for most of them.
The general practice for many years past among naturalists has been to restrict the terms "Insecta" and "insect" to the class of Arthropods with three pairs of legs in the adult condition: bees, flies, moths, bugs, grasshoppers, springtails are "insects," but not spiders, centipedes nor crabs, far less earthworms, and still less slugs, starfishes or coral polyps.
A species of bristle-tail (Machilis maritima) and quite a number of springtails haunt the sea-coast at or below high-water mark.