42 BULLETIN 1369, U. 8. DEPARTMENT OF AGRICULTURE 
number depends to some extent upon whether the fly is disturbed 
during the process of oviposition and also upon the length of the — 
hair. In the case of H. bovis the eggs are always deposited singly 
on the hair. 
DISTRIBUTION OF EGGS ON HOST 
fH. lineatum shows a marked tendency to oviposit on the heels of 
cattle which are standing, the favorite place apparently being the 
short hair overhanging the rear of the hoof and between the hoof 
line and the dewclaws. Many eggs, however, are deposited higher 
on the legs in the region of the hocks and a few above the hock line. 
Some eggs are also deposited on the belly, flanks, and forelegs, and 
occasionally on the sides, shoulders, and neck. In practically all of 
the writers’ observations of depositions on cattle which are not lying 
down, it seems evident that many of the eggs deposited elsewhere | 
than on the heels are laid after the fly has been disturbed by the © 
actions of the host. Many eggs are also deposited along the es- — 
cutcheon, on the outside of the thighs, on the tail, and on the base of 
the udder, and some along the side and on the forelegs in the region 
of the elbow joint. Infestations in these regions are especially com- 
mon among quiet stock, oviposition taking place while they are 
lying down. In one instance over 200 fresh eggs were found attached 
to the hair on an area not over 2 inches square just behind the upper 
end of the scapula. The writers’ observations on flies in nature and 
upon those placed on hosts in captivity indicate that they prefer the 
short, comparatively coarse hairs to the long, dense, silky ones. 
H. bovis also prefers the heel or lower leg for a place of attach- 
ment for its eggs, but since this species frightens the animals much 
more, and since the flies continue to follow the cattle, depositing eggs 
while pursuing the rapidly running animals, a much larger per- 
centage of eggs is deposited higher on the legs, especially in the 
region of the thighs and on the rump. Although a considerable 
number of eggs are laid on other parts of the body, especially along 
the sides, they tend to be concentrated on the hind quarters. 
METHOD OF ATTACHMENT OF EGGS 
As has been indicated under its description, the egg is provided 
with a definite attachment area or clamp. In addition to the place- 
ment of the clamp around the hair, each egg appears to be provided 
with a cement which when dry firmly glues it to the hair. Eggs 
have been observed to remain attached on the host for several weeks, 
sometimes the distal end gradually breaking away so as to leave 
only a portion of the shell. As shedding of the winter coat usually 
takes place about the time the eggs are deposited, many of them 
are shed off and perish before they have had an opportunity to 
hatch. 
The eggs are nearly always attached very close to the skin, and 
this renders them inconspicuous, as they are usually covered by the 
overhanging hair. This is particularly true of H. bovis. 
INCUBATION 
The incubation period of H. lineatum, as observed in many lots 
of eggs kept under varying conditions, was found to range from 
