﻿THE CATTLE GBUBS OR OX WAEBLES . 35 



posited on the heels developed grubs in the back. One had 45, with 

 about an equal number on each side of the backbone, and the other 

 had 2 when the animal was disposed of on December 23. Possibly 

 other grubs would have come up later. The animals to which the 

 young larvae were fed was observed throughout the fall and winter 

 and no larvae whatever came to the back. 



In 1919 11 animals were* used in the tests. Four of these (Nos. 

 411, 412, 413. and 415) received eggs on the heels and front feet, 

 one near the hips (Xo. 419), and three on the heels and elsewhere 

 (Xos. 409, 410, and 414). Three (Nos. 416, 417, and 418) were 

 fed eggs and newly hatched larvae. One of those receiving eggs 

 on the heels and elsewhere (Xo. 410) was killed shortly after the 

 eggs began to hatch in an effort to determine the presence of larvae 

 in or under the sldn. Xo larvae 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 larvae are present. On July 9, one 

 of those animals which received eggs on the heels, front feet, hock, 

 and side of abdomen (Xo. 409) was killed and examined; 76 larvae 

 were found along the gullet. One of the animals which received 

 eggs on the heels and front feet (Xo. 411) was killed October 7 

 and no larvae 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 

 larvae. 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 eggs on the hips only (Xo. 419) developed a total of 13 grubs 

 the following winter, and the one having the eggs ])laced on the 

 hock, front feet, and udder (Xo. 414) developed a total of 20. On 

 the other hand, two of the animals (Xos. 417 and 418) Avhich re- 

 ceived fertile and Avell-iucubatcd eggs, as well as healthy larvae, 

 by way of the moutli. failed to dcA'elop a single grub during the 

 subsequent fall and winter. Tlie third (Xo. 416) was killed July 

 9, and a careful dissection failerl 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 

 wei-e employed. Three of these (Xos. 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 toj) of (he shoulders; two (Xos. 158 and 22) 

 had the eggs placed on the front and rear legs and on the belly 

 near the flank: anfl two (Xos. UiO and 414) received lai'va^ and eggs 

 by way of the month. Two otliei- animals (Xos. 92 and K23) were 

 used to test the migratory tendencies of the second-stage larvio, which 

 were removed from the gullets of slaughtered cattle. These were 

 inserted in pockets cut under Hie skin near the hock. 



