Many species of the _Dexinæ_ are of the most metallic-green or blue. They are principally found in Australia. The Flesh Fly (_Sarcophaga carnaria_) belongs to the _Sarcophaginæ_ and is one of our largest species. The _larvæ_ of some species are called "Screw Worms" in America. The fourth sub-family, the _Muscinæ_, contains the most typical species of the _Diptera_ or two-winged flies. The common House Fly (_Musca domestica_) is the most familiar example. Several blue-and-green flies are produced from _larvæ_ which feed on more or less putrid flesh, and are well known to anglers as "Gentles." The Blow Fly or Blue Bottle (_Musca vomitoria_) is one of these, also the Green Bottle Fly (_Lucilia Cæsar_) which is often common about hedges in the summer time. Many species belong to the sub-family _Anthomyiinæ_, are very small insects, and their _larvæ_ mine in the leaves of plants like those of _Tineæ_. [Illustration: Fig. 150.--Platypeza Fasciata (Mag.)] [Illustration: Fig. 151.--Gastrophilus Equi (Mag.)] Section 2, namely _Acalypteræ_, contains eight sub-families. The species of _Scalophaginæ_ are usually called "Dung-flies." The commonest species, the Yellow Dung Fly (_Scatophaga stercoraria_), feeds largely on manure and other refuse. The _Ortalinæ_ are flies of small or moderate size, which are met with principally in woods and fields. The _Trypetinæ_ feed chiefly on fruit. One species, _Ceratitis hispanica_, is very destructive to oranges in the south of Europe, etc. Of the _Piophilinæ_, _Piophila casei_ may be taken as the typical example. The _larvæ_ which abound in cheese and bacon are popularly called "Cheese Hoppers," or "Jumpers," in allusion to their habit of springing. The _Diopsinæ_ are principally met with in the tropical parts of the world. They are generally insects of moderate size. Most of the species of _Chloropinæ_ are of small size. Their _larvæ_ generally live in the stems of corn and various kinds of grasses. The _Drosophilinæ_ are small, dull-coloured flies, the _larvæ_ of which feed on fungi, rotten fruit, and similar substances. [Illustration: Fig. 152.--Hypoderma Bovis (Mag.)] The last sub-family, namely, the _Agromyzinæ_, is very extensive. One of the commonest species is _Phytomyza ilicis_, the _larva_ of which forms large brown blotches on the leaves of the holly. [Illustration: Fig. 153.--Diopsis Subfasciata (Mag.)] _Family 35, Phoridæ._--The insects belonging to this family are generally of small or moderate size. They are very active, and may be observed on plants, and also sometimes sunning themselves on windows. TRIBE III.--HOMALOPTERA. The insects belonging to this section much resemble spiders in appearance. They are all parasitic, and are remarkable for the perfect insect producing its young singly, and that not in the egg state, as in most insects, but either in the _pupa_ state, or as a mature _larva_ ready to become a _pupa_ immediately. This tribe contains only three families.