The legs are slender and moderately long, or short and stouter, and are frequently sexually dimorphic—the commonest form being the enlargement of the protarsi; in other forms the mesotarsus (fourth joint) is enlarged, or femora, tibiae, or coxae are unusually developed. The claws and pulvilli are well developed.

In the wings (fig. 1) there is a certain amount of variation of shape and venation. The anal angle may be strongly or moderately developed or altogether wanting; vein Sc either meets the costa or evanesces toward its apex; R₄ and R₅ either branch or are fused throughout. When branching, R₄ leaves R₅ at an acute or right angle, and in some cases is recurved to meet the costa; in one genus (Blepharoprocta, not yet recorded in New Zealand) it joins R_{2 + 3} and not the costa, the recurving being an approach to this state. In some species M₁ and M₂ are wholly or partially fused after leaving cell 1st M₂, and when completely fused may not quite reach the wing-margin. Cu₂ is either recurrent, being more or less parallel with the posterior margin when it is confluent with 1st A, or forms an acute or right angle with 1st A, which at times is more or less completely evanescent, as is sometimes also cell Cu. In many of the Empid wings there is a spurious vein, similar to that of the Syrphidae, running through cells R and R₅; cell 1st M₂ is rectangular, triangular, or narrowed apically, while in some genera (not yet known in New Zealand) it is completely wanting.

The abdomen is more or less robust or slender. The genitalia of the male vary considerably; in some species they are more or less concealed, in others prominent and knob-like. The most unique forms are found in the genus Hilara; in many of these flies there is a sheath-like appendage frequently almost as long as the body itself (fig. 2) or much shorter. A dissection of this appendage—which I refer to as the “genital appendage”—shows that it is the sheath of the penis, which is extremely long, the genitalia being attached to it on each side on the upper side at the base. This appendage is blade-like, being laterally compressed, and the penis, which is a flexible, chitinous, thread-like structure, leaves the abdomen vcntrally and runs around the edge of the sheath, entering and projecting beyond the genitalia on the dorsal anterior angle of the sheath (fig. 2); the penis is retracted within the genitalia by being drawn upward from the lower edge of the sheath to the upper, as shown by the dotted line. When at rest the genitalia are enclosed (fig. 2a) beneath the dorsal plate of the third-last abdominal segment, the penultimate and ultimate being

much shortened in height to receive the genitalia. The female abdomen ends in a pair of stylets, and when the apical segments are extruded they appear as shown in fig. 3. In some species the membrane of the third abdominal segment of the female on each side may be inflated to form a bilobed bladder (fig. 4), the membrane when not inflated forming a whitish wrinkled patch. These peculiar bladders have apparently to do with the aquatic habits of the species, since Mr. J. W. Campbell, who found the specimens, states that the flies (Hilara flavinceris n. sp.) were found beneath an overhanging rook above a stream.

The vestiture consists of bristles and hairs, the former arranged in definite systems which are beyond doubt of considerable taxonomic value, and in one or two genera a supplementary synopsis of the species has been drawn up, based on the thoracic and occipital chaetotaxy of the males. It is apparent from the material available that the chaetotaxy of the two sexes in the same species varies to a greater or lesser degree, and when a more complete series of specimens and species is procured a more definite account will be drawn up. The occiput is usually bristly above the foramen and hairy below; ocellar bristles are usually present and also delicate frontal ones; the first and second antennal joints are bristly or haired, and in some forms there are bristles or hairs on the face; the palpi are bristly or haired. On the dorsum of the thorax the bristles are either well developed or delicate and small, the acrostichals and dorso-centrals frequently being represented by one or more rows of small bristles which usually lengthen posteriorly, the dorsocentrals often ending in a pair of well-developed bristles. The bristles on the prothorax show important variations. The scutellar bristles may be strong or weak, erect or horizontal, and vary greatly in number; they are usually marginal, but discal ones are sometimes present. There are bristles or hairs on the metapleurae of many species. On the wings there may be one or more strong costal bristles near the articulation. The bristles of the legs, when present, are variable; in some species they are large and strong, or short and thorn-like, arising from swellings on the under-side of the femora; the coxae may also be strongly bristled or haired, while on the tibiae are long or short spines; on the lower side of the front protarsi may be a row of minute teeth-like spines. The bristles of the abdomen are usually hair-like, but more conspicuous along the posterior margins of the segments.

The Empididae are predaceous and great hunters; none of them is large, and many are very small; their colours are inconspicuous. They are frequently found skimming over the surface of calm water, or dancing in swarms in the air; other species are solitary. Representatives of the family occur under most conditions, particularly on the foliage of bushes near water, or upon the rocks of streams; certain forms occur on sandy sea-coasts. The life-history of the family is but little known. The larvae of some have been found in the ground and among decaying vegetable matter, and it has been noted that some are carnivorous. It is probable that certain species are semi-aquatic, since a species of Hemerodromia has been found in the mud of a stream (Lundbeck).

The writer, while dissecting the abdomen of the female of Hilara flavinceris n. sp., found the ovaries filled with yellowish-brown eggs, each of which is oval with one end truncated and surrounded by a narrow rim (fig. 5); this end is covered by a whitish granular membrane from the middle of which is the micropilar projection (fig. 6); the surface of the egg is sculptured by hexagonal depressions.