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Rh four hairs, of which one is far longer than the others; other symmetrically arranged hairs also occur. In the middle line is the proboscis; this consists of two lateral, moveable, palp-like structures, each bearing hairs and terminating in a stout bristle. These structures are presumably the maxillary palps. Then there is a median very mobile structure, which is the sucking tube; this moves in all planes, and may be protruded or withdrawn. Its mouth shows a somewhat plicated orifice, and behind it undoubtedly ends in a sucking pharynx. This median structure is probably homologous with the second maxillse or the labium.

The feet of the Grouse-fly are large but very beautiful. In Pl. LV ., Fig. c., will be found a coloured sketch of a foot seen obliquely. From this drawing it will be seen that the large paired claws are double, and that whereas the distal limb of each claw is slender, and very sharply pointed, the proximal limb is much stouter and ends bluntly. Between the claws is a median, feathered process with hairs or bristles, and at the base of each double claw is a pulvillus covered with minute hairs.

We do not know the exact relations of the Grouse-fly to the Grouse. It is believed to suck its blood, and it will certainly bite human beings. For a time it seems to burrow amongst the feathers of the bird, and any one handling Grouse during the summer is likely to disturb a fly or two. They come buzzing out, and are apt to crawl up one's sleeve by aid of the pair of great hooked claws on their feet. Altogether they have a sinister aspect, and to people who do not like flies they are very repellent. They occur freely in larders where freshly-killed Grouse have been placed, and after a short time they leave their dead host and accumulate upon the windows.

The earliest month in which we have found the Grouse-fly is June. The latest we have found it up till the present time is September. In Caithness they have been taken as late as October. Perhaps they are most plentiful in August.

The females seem to be commoner than the males, or, it may be in August they are more readily taken. Like other members of the Hippoboscidse, which includes the horse-fly, forest-fly, and sheep-tick, the Grouse-fly does not lay eggs, but the ovaries produce one large ovum at a time, and this passes into a dilated oviduct which acts as a uterus, and here the egg develops. After attaining a certain stage of development, the larva surrounds itself with a pupa-skin, and is extruded. The chitin covering the larva hardens and blackens with exposure to the air, and forms the so-called pupa-case; in fact, one may almost say the young are hatched as pupæ. At no time is the larva exposed, though there is a larval stage free in the uterus wrapped first in the egg-shell and then in the pupa-case.