The thorax is not so distinctly divided into the three segments as in some other insects, nor the parts so well defined as in the hymenoptera; the wings, transparent or parchment-like, are seldom coloured; the legs, usually not thickened, are furnished with five tarsi, and well developed claws, with a small pad under each, known as the pulvillus. The abdomen is composed of a variable number of segments ranging from four to nine, but in the former case though not visible the terminal ones are probably absorbed into the anal tube at the extremity. Most diptera are brown, black, or grey, though metallic tints predominate in some families; and are clothed with short scattered hairs or bristles. The typical fly larva is an elongated legless maggot with the head portion slender, enclosing a pair of black retractile hooked jaws, with tracheae opening behind and running through to the broadened anal segment where they form small rosette-like processes round the external aperture. The eggs are laid in all kinds of decaying vegetable or animal matter, with the exception of the few that produce galls, or otherwise damage plant tissue; when full grown they change into a hard shell-like chrysalis, the tip of which is pushed off by the perfect fly when ready to emerge. Though this country is very rich in Diptera and many cosmopolitan species have been introduced such as the house flies, they have been much neglected by Australian collectors and entomologists. The Diptera are divided into two large sections, which are further subdivided into four main groups, to which a fifth has been lately added for the reception of the fleas, which however are often placed by specialists in a class by themselves (_Siphonaptera_). The older writers subdivided them into about 70 families but latterly these have been reduced, and most of our species will come under about 30 families, of which I can only note our most striking representatives. In 1830 the French naturalist Robineau Desvoidy published his “Essai sur les Myodaires,” in which some of our species were described. Between the years 1834 and 1835 Macquart brought out his “Histoire naturelle des Insectes Diptères” (forming part of the great French work Suites à Buffon), followed (1838–42) by his “Diptères exotiques, nouveaux ou peu connus” comprising two volumes and many plates, with 5 supplements (1846–55). Walker between 1848 and 1855 compiled a “Catalogue of the Diptera of the British Museum” consisting of 7 volumes; and others are described in his “Diptera Saundersiana” 1856.