The Book of the Fly / A nature study of the house-fly and its kin, the fly plague and a cure

by George Hurlstone Hardy

A = the Head, comprising nine regions and parts (A, I to A, IX).

A, I, the Vertex, which contains (1) the Ocellar Triangle; (2) the Ocelli; (3) the Vertical Triangle, a coloured patch surrounding the ocellar triangle; (7) the Vertical Orbit, the sides of the vertex close to the compound eyes. The Bristles hereabouts are (4) the Vertical (inner and outer); (5) the Post-vertical; and (6) the Ocellar.

A, II, the Compound Eyes, large and often hairy.

A, III, the Frons is the forehead between the eyes; it contains (1) the Frontal Stripe; (2) the Frontal Orbits at the sides of the frontal stripe; (3) the Frontal Lunule (plate VII, 5) a crescent immediately above the antennæ. The Bristles hereabouts are (4) one pair of Frontal; a row, or rows of (5) Fronto-orbital; and (6) Lower Fronto-orbital. The (7) Eye Margin is a narrow, often glistening, white line close to the eye.

A, IV, Antennæ, jointed processes springing from between the eyes just below the frons; those with numerous joints are illustrated in plate II, others in plate III. The Frontal Suture in the middle of the face is a little pit in which short antennæ often lie close together. The (1) Basal Joints are the two next the head; (2) the Flagellum, all the joints, when numerous, taken together; (3) the First Joint is next the head; (4) the Second Joint; (5) the third Joint (plate III, 1-9) is sometimes ringed; (6) the Arista, or Seta, is a plume, spine, or bristle springing from the third joint at some point of its upper surface between the base and the tip.

A, V, the Face is the region above the so-called mouth and below the antennæ; the ridges bounding the face on each side are (1) the Facialia; here are (2) the Facial Bristles; (3) the Mystax (pl. VI, fig. 28) is peculiar.

A, VI, the Cheeks, spaces at the sides between A, II and A, V (I).

A, VII, the Jowls, parts below A, VI and the so-called mouth.

A, VIII, the Mouth, more or less of a cavity into which (3) the Proboscis (the jointed sucking trunk) can be sometimes partly withdrawn; the proboscis has a basal joint called the Rostrum (a snout); the other joint is called the Haustellum (a pump) and has the tip variously adapted as for mere surface suction, or for deep insertion, or for piercing. (1) the Peristome is the region surrounding the mouth; (2) the Vibrissæ are strong bristles close to the sides of the mouth, or A, V (I); (4) the Palpi, two feelers (or perhaps smelling organs) attached to the proboscis.

A, IX, the Back of the Head; here (I) Post-orbital Bristles are sometimes found, that is to say, behind the eyes, A, II.