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the Mouth, more or less of a cavity into which (3) the Proboscis (the jointed sucking trunk) can be sometimes partly withdrawn; the proboscis has a basal joint called the Rostrum (a snout); the other joint is called the Haustellum (a pump) and has the tip variously adapted as for mere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. B = the Thorax, the middle portion of the fly bearing the organs of locomotion. B, I, the Dorsum. The diagram on _plate_ VI, _fig._ 40 illustrates the upper surface of this region; this part is bounded in front by (_a_) the Neck; behind by (_b_) the Scutellar Suture (15) or Seam; at the sides by (_c_) the Dorso-pleural Sutures (9-9) running from the front corners to the front of the Wing Bases; by (_d_) the Wing Bases (10-10); and by (_e_) the Scutellar Bridges, which are ridges (11-11) running with right and left inclines to the root of (6) the Scutellum. The Dorsum is crossed by (8) the Dorsal Suture, behind which are the Alar Regions (5-5); here on each side is a ridge (12-12) the Alar Frenum; rows of minute bristles on the centre are termed Acrostichal. B, II, the Sides, or Pleuræ, specified separately in connection with—