THE CATTLE GRUBS OR OX WARBLES 35 
posited on the heels developed grubs in the back.. One had 45, with 
‘a about an equal number on each side of the backbone, and the other 
had 2 when the animal was disposed of on December 23. Pessibly 
other grubs would have come up later. The animals to which the 
young larvee were fed was observed throughout the fall and winter 
and no larvee whatever came to the back. 
In 1919 11 animals were used in the tests. Four of these (Nos. 
411, 412, 418, and 415) received eges on the heels and front feet, 
one near the hips (No. 419), and three on the heels and elsewhere 
(Nos. 409, 410, and 414). Three (Nos. 416, 417, and 418) were 
fed eggs and newly hatched larve. One of those receiving eggs 
on the heels and elsewhere (No. 410) was killed shortly after the 
egos began to hatch in an effort to determine the presence of larvx 
in or under the skin. No larve were found but some small holes 
were clearly visible in the skin beneath one group of the eggs, and 
the connective tissue under the eggs was yellowish and edematous, 
just as it appears when the larve are present. On July 9, one 
of those animals which received eggs on the heels, front feet, hock, 
and side of abdomen (No. 409) was killed and examined; 76 larvee 
were found along the gullet. One of the animals which received 
egos on the heels and front feet (No. 411) was killed October 7 
and no larve were found owing, it is believed, to the fact that 
the eggs were infertile. In the case of this animal no irritation 
or lesions indicating penetration were observed, after what should 
have been a normal period of incubation. All of the 112 eggs de- 
posited on this animal were laid by one fly and some of the eggs 
clipped from the host and placed in an incubator failed to develop 
Jarve. Of the other three receiving eggs on the heels and front 
feet, all showed moderate infestations of grubs (average of 14.3) 
in the back the following fall and winter. The animal receiving 
the eges on the hips only (No. 419) developed a total of 13 grubs 
the following winter, and the one having the eggs placed on the 
hock, front feet, and udder (No. 414) developed a total of 20. On 
the other hand, two of the animals (Nos. 417 and 418) which re- 
ceived fertile and well-incubated eggs, as well as healthy larve, 
by way of the mouth, failed to develop a single grub during the 
subsequent fall and winter. The third (No. 416) was killed July 
9, and a careful dissection failed to reveal the presence of a single 
larva in the gullet or elsewhere. 
In the tests begun in the spring of 1920 10 experimental animals 
were employed. Three of these (Nos. 167, 159, and 417) were in- 
fested on the legs, mostly on the hind ones from the hock down; one 
received eggs only on the top of the shoulders; two (Nos. 158 and 22) 
had the eggs placed on the front and rear legs and on the belly 
near the flank; and two (Nos. 160 and 414) received larve and eggs 
by way of the mouth. Two other animals (Nos. 92 and K23) were 
used to test the migratory tendencies of the second-stage larvee, which 
were removed from the gullets of slaughtered cattle. These were 
inserted in pockets cut under the skin near the hock. 
