DIPTERA. 53 
taking up the same immovable position, and in each of these 
movements turning the head to the opposite way from that in 
which they are going. This naturalist is certain that on these 
occasions they are watching for the females, which they dart 
upon. When they have succeeded in doing so, they rise so high 
as to be out of sight. 
To this group belongs the genus Tadanus. 
The first species we shall mention, Tabanus autumnalis (Fig. 
33), a common species, is eight or nine lines in length, and of 

Fig. 83.—Tabanus autumnalis. Fig. 34.—Chrysops cxcutiens. 
blackish colour. The palpi, the face, and the forehead are grey ; 
the antenne black; the thorax grey, striped with brown; the 
abdomen spotted with yellow, the legs of a yellowish white, and 
the outer edge of the wings brown. 
Another species (Tabanus bovinus) is twelve lines in length, and 
of a blackish brown. The palpi, the face, and the forehead are 
yellow; the antenne black, with a whitish base; the thorax, 
covered with yellow hair, is striped with black; the posterior 
edge of the segments of the abdomen pale yellow; the legs 
