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 counted. 



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 anal, is provided around its anterior margin with from 5 to 10 rows of short 

 spines. Along the venter this strip of spines consists of about 10 rows and 

 along the dorsum of about 5 rows. The anterior end of the first thoracic seg- 

 ment is armed with spines for about one-third of its length. These spines and 

 the ones in the spinose strips around the other two thoracic segments appear 



