. Bulletin of the Department of Agriculture. Agriculture; Agriculture. HORSE-FLIES A1STD WESTERN AGRICULTURE. 13 to the base of the mass the eggs slant at an angle of about 45°, the mass usually being placed so that the distal end of the eggs points downward. A freshly laid mass is almost snow white. In a few hours this deepens to a whitish gray and becomes progres- sively darker, until on the third or fourth day it is nearly light brown. After hatching, the mass is light to dark brown. The mass is covered with a cement which helps to hold the eggs firmly together and possibly gives them
. Bulletin of the Department of Agriculture. Agriculture; Agriculture. HORSE-FLIES A1STD WESTERN AGRICULTURE. 13 to the base of the mass the eggs slant at an angle of about 45°, the mass usually being placed so that the distal end of the eggs points downward. A freshly laid mass is almost snow white. In a few hours this deepens to a whitish gray and becomes progres- sively darker, until on the third or fourth day it is nearly light brown. After hatching, the mass is light to dark brown. The mass is covered with a cement which helps to hold the eggs firmly together and possibly gives them some protection against predators and parasites, though the eggs of this species are heavily parasitized, as is discussed on page 31. The number of eggs in a mass varies from 200 to 800. The number of eggs was ascertained by counting the issuing larvae, and since the masses in all but one case were para- sitized the count of larvae did not accurately indicate the number of eggs. The mass not parasitized contained 582 eggs. From one slightly parasitized mass. No. 7694, 701 larvae were Fig. 9.—Along western shore of Alkali Lake, showing location of egg masses of Tabanus punctifer. Larva. Before hatching the larva of Tab anus punctifer is ready to cast the skin of the first instar. Through the transparent eggshell can be seen the second instar within the exuvium of the first. Most of the larvae when hatching carry the first exuvium to the water, where the molt is completed. The larvae remain near the top of the water with the siphon to the surface. DESCRIPTION OF THE FIRST EXUVIUM. "The first exuvium is 2 millimeters long. There are 11 body segments, 3 thoracic and 8 abdominal. The thoracic segments taper to the narrow diameter of the head capsule. The anal segment terminates with the pointed siphon, which, like the mouth parts, is shed when the larva molts. To many of the skins the molted siphon and mouthparts are hanging. Each segment, except the eleventh or an
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