8 
ee 
a 
THE CATTLE GRUBS OR OX WARBLES 33 
The fly of H. bovis (fig. 20) is considerably larger and much stouter than that 
of H. lineatum. This is especially true of the thorax, which is much broader. 
The color is similar to that of H. lineatum, but the band of yellowish hairs 
across the prothorax dorsally is markedly wider and the shade slightly deeper 
than in H. lineatum. The shiny longitudinal lines of the thorax are obscured 
anteriorly by the hair. The color of the abdominal vestiture is similar to that 
of H. lineatum except on the terminal segments, which have a wider and more 
and yellow hairs, and the tarsi are brown 
sharply defined band of lemon yellow, distinctly paler than in H. lineatum. 
The wing veins of H. bovis are of a reddish-brown color. The femora and the 
tibize are black and well covered with black 
and much less hairy than in H. lineatum. 
HOW THE LARV# OF HYPODERMA 
LINEATUM GAIN ENTRANCE TO 
THE HOST 
The method of ingress of various se 
animal parasites is often a point of wee | 
considerable economic importance. Fic. 17—Hypoderma lineatum: Pos- 
As has been indicated in the historical oe ue eel Laue 
sketch, the opinions held by various 
investigators in regard to the way in which Hypoderma larvee enter 
the host have been at wide variance; and even up to the present time 
there are but few who feel certain of the method of ingress of these 
parasites. 
During 1916 plans were laid at the Dallas laboratory to carrry out 
a series of tests to determine accurately the way in which the larvee 
enter the host. These tests have been continued along similar 
lines up to date. Since a full knowledge of the habits of oviposition 
of adult H. lineatum has been gained, it is evident that there are 
really only two ways in which the larve might get into the host, one 
of these being by direct penetration through the skin and the other 
by being taken in by mouth in the egg or young larval stage. 
The following plan, with slight modification, was carried out in 
all of the tests: Certain animals were placed in fly-proof cages and 
thus protected from all possibility 
of attack by heel flies during the 
season of fly activity. To these 
animals were administered by 
mouth the eggs of newly hatched 
larve. Most of these were ap- 
plied to the tongue or inside of 
the lips of the host, but some were 
placed in capsules and the host 
made to swallow them. Certain 
Fic, 18—Hypoderma bovis: Posterior of these animals were dissected 
Gereatly ehinreed (Gasket a time when the Jarves should 
be present in the gullets or other 
portions of the carcass commonly infested, to ascertain if possible 
whether any of them escaped from the digestive tract. Others 
were kept and watched the following fall, winter, and early spring 
for the appearance of larve in the subdermal tissues of the back. 
At the time that these animals were being fed with the larve and 
eggs, others were infested on the legs or elsewhere by allowing 
flies captured in nature or reared in cages to deposit eggs upon 
58252 °—26——_3 
