The older naturalists used the word ""insect"" to denote any terrestrial Arthropod. To-day the word has this significance in the vulgar tongue. The boundaries of the ""Class Insecta"" are by no means clearly defined: Handlirsch in 1908 broke up the hexapod insects into four ""Classes"", while to-day the six legged Myrientomata are bandied about between the ""Insecta"" and the ""Myriapoda"", so that no certainty exists as to the significance of the Entomological term ""Insect"" .
On bright sunny days the flies (Plate I) may be seen, here and there, sunning themselves on the upper sides of leaves, making short runs from side to side while moving their wings, each alternately, backwards and forwards. Where there is honey-dew they go to feed, and females may be seen on the host-plant, searching for flowers in which to oviposit.
One of the chief aims in drawing up descriptionptions is uniformity and what finally proved the most satisfactory method was to write out a straight-forward descriptionption, using contractions and starting each item on a fresh line, beginning at the head. Both supplementary to, and instead of this, various charts were tried and the one shown on Chart V was used for the present series. Such charts are not entirely satisfactory as the amount of detail needed to be recorded for any particular character varies from species to species, and different charts are needed for the various groups of Trypetidae.