The Diptera larvae can be divided from an ethnological point of view into four categories: and the members of each, though of diverse systematic affinities, possess in common certain structural characters, which Keilin (1912) considers to be adaptations to the manner of life. The categories are as follows: (i) Saprophagous larvae: those which feed on decayed vegetable matter or the excrement of herbivorous animals; these have a buccal armature similar to that of Calliphora or Lucilia: the ventral surface of the basilar piece is feebly chitinized and has a number of longitudinal ridges projecting into the lumen of the pharynx. (ii) Phytophagous larvae, which feed on living plants, as leafminers, root-miners, etc.: these have the bucco-pharyngeal armature more concentrated, the basilar piece more chitinized, with ridges feebly developed or absent, the mandibles modified as several toothed scrapers. (iii) Parasitic larvae: their buccal armature resembles that of parasitic Tachinidae. (iv) Parasitic larvae—carnivorous larvae: It is now known from the researches of Portchinsky (1910), and later of Keilin himself, that a good number of larvae found in excrement are not really coprophagous, but live on other larvae or other small animals found with them in the excrement. These carnivorous larvae attack their prey, perforating its skin, and sucking its contents. For instance, the larvae of Graphomyia maculata, found in liquefied decomposing vegetable matter, feed on larvae of Eristalis and pupa of Tipulidae, those of Calliophris riparia, found among moss, feed on small oligochaete worms and larvae and pupae of Psychodidae. These carnivorous larvae have certain characters in common. Thus the mandibles are sharp, piercing hooks and the basilar piece of the armature is very long, narrow and strongly chitinized and entirely without the internal longitudinal ridges.” (Scott, 1915.)