[Illustration: Fig. 106—_Trichopteryx fascicularis_. Britain. A, Outline of perfect Insect; B, part of upper surface; C, larva from side; D, from above; E, pupa; F, wing; G, natural size of imago.] FAM. 21. TRICHOPTERYGIDAE.—_Extremely minute: antennae {228}clavicorn (basal and apical joints thicker than middle joints); tarsi three-jointed; elytra sometimes covering abdomen, in other cases leaving a variable number of segments exposed; wings fringed._ This family comprises the smallest Insects; _Nanosella fungi_ being only 1/100 of an inch long, while the largest Trichopterygid is only 1/12 of an inch. The small size is not accompanied by any degeneration of structure, the minute, almost invisible forms, having as much anatomical complexity as the largest Insects. Very little is known as to the natural history. Probably these Insects exist in all parts of the world, for we have about eighty species in England, and Trichopterygidae are apparently numerous in the tropics.[108] FAM. 22. HYDROSCAPHIDAE.—_Extremely minute aquatic Insects, with elongate abdomen. Antennae eight-jointed._ The other characters are much the same as those we have mentioned for Trichopterygidae. The family is not likely to come before the student, as only three or four species from Southern Europe and North America are known.[109] [Illustration: Fig. 107—A, Larva of _Orthoperus brunnipes_ (after Perris); B, _O. atomarius_, perfect Insect. Britain.] FAM. 23. CORYLOPHIDAE.—_Minute beetles. Tarsi four-jointed, but appearing only three-jointed, owing to the hind joint being concealed by the emarginate (or notched) second joint. Six free ventral segments. Maxillae with only one lobe. Antennae of peculiar form._ There are about 200 species of these little Insects, but the family is apparently represented all over the world, and will probably prove to be much more extensive. The peculiar larva of _Orthoperus brunnipes_ was found abundantly by Perris in thatch in France. Mr. Matthews proposes to separate the genus _Aphanocephalus_ as a distinct family, Pseudocorylophidae.[110] In Corylophidae the wings are fringed with long hairs, as is the case in so many small Insects: the species of _Aphanocephalus_ are rather larger Insects, and the wings are not fringed; the tarsi are only three-jointed.