The Insects of this order are closely related to those of the preceding, but the long anal bristles do not form a "spring;" and the mouth is distinctly masticatory. The two principal genera are Lepisma and Campodea (fig. 180, C), both of which live generally under stones or in dark situations. The body is hairy, or clothed with metallic scales; these latter organs being in Lepisma so delicately marked that they are commonly used as test-objects for the microscope.
According to Packard, the Thysanura and Colletnbola are to be regarded as degraded groups of Neuroptera, the former having also affinities with the Myriapoda. According to Sir John Lubbock, Campodea may be regarded as a modern representative of an ancient type-form, from which the higher Insects originally took their rise.