THE CATTLE GRUBS OR OX WARBLES 59 
spiracle to the hole and almost perpendicular to it. Thus the hole 
in the skin is always near the posterior end of the larva, which may 
have the anterior portion in any direction. The majority of the 
cysts have the aperture near the upper side. 
TOTAL DEVELOPMENTAL PERIOD IN THE BACKS OF CATTLE 
As with other stages of Hypoderma, there is a variation in the 
total period required for the development of the larve from the time 
the holes are cut through until the larval growth is completed. The 
determination of this period with accuracy is of much importance 
in control and especially in eradication work, since the interval 
between treatments 
should be governed 
by such data. 
In a large num- 
ber of cattle of sev- 
eral breeds warbles 
of both species were 
followed through 
their entire develop- 
ment in the subder- 
mal tissue. Owing 
to the high mor- 
tality among the 
larve, especially 
when examined re- 
peatedly to deter- 
mine molts,_ etc., 
only a comparative- 
ly few records of 
complete develop- 
ment were obtained 
among the hundreds 
of warbles observed. 
In order that the 
duration of the lar- 
val stages might be 
determined various 
individual cattle Fie. 28.—Headlight outfit used He examining cattle grubs 
in cysts 
were observed from | 
the time warbles began to appear until all grubs had made a normal 
egress. These observations were made as frequently as time would 
permit, usually once each day. Through practice the touch was 
developed to a high degree and one could readily detect the first 
indication of a foreign object under the skin or a minute amount of 
exudate from a puncture of the skin. 
In making the examinations a headlight was developed which 
proved of great value (fig. 28). It consisted of a shortened flash 
light attached to a head band, and served by two dry cells carried 
on a belt. The focus was adjusted to permit the observer to use a 
hand lens. 
With the younger stages of the larve in particular it was found 
necessary to apply pressure around them to force them toward the 
