THE CATTLE GRUBS OR OX WARBLES Do 
ing of larve along the ribs, on the diaphragm, and in the neural 
_ canal indicates that they pass from the gullet across the diaphragm 
.| to the ventral ends of the ribs and thence follow the connective 
}/| tissue beneath the pleura up to the back. Some probably work their 
| way between the muscles and pass directly up the diaphragm from 
the gullet to the back. A number of these no doubt gain entrance to 
the neural canal, later pass out through the posterior foramen, and 
_ then go up to the connective tissue beneath the skin along the back. 
| Both of these routes are probably followed in migrating from the 
)/ gullet to the back. 
_ The writers’ observations indicate that the migration from the 
_ gullet to the back is rather rapid. The first larvee begin to appear 
_ in the subdermal tissues of the back very soon after the maximum 
_ size has been reached in the gullet. As soon as the number of larve 
|) are observed to decrease in the gullet they are observed to appear 
on the back, with practically no increased growth. 
| Unfortunately it has not been possible carefully to dissect ani- 
mals infested only with H. bovis so as to determine just where the 
| larvee occur from the time they enter the host until they appear 
on the back. In New York, where both species are present, the new= 
ral canals of 140 slaughtered animals were examined and all the 
larve found were H. bovis. Thirty specimens were located, with 
-a maximum of four in one canal. Larvee were found in this situa- 
‘tion during the months of October to March inclusive. The size 
ranged from 6.5 to 14 millimeters, the larger ones being found later 
in the season. 
At Dallas, Tex., Cabere HT. lineatum only occurs, about 75 beeves 
were examined rather carefully as they were dressed. Only one 
_ Hypoderma larva was found in the neural canal, a third-stage speci- 
men located in the central portion of the second lumbar vertebra 
and measuring 14 millimeters in length. 
This observation indicates that the larve of H. bovis enter the 
neural canals of cattle more frequently than do those of @. lineatum. 
It seems unlikely, also, that all larve found in this situation are 
en route directly to the back, as the larve found during October 
were only from 6.5 to 9 millimeters long, and never have such small 
larvee been encountered in the subdermal tissues of the back. Fur- 
thermore, the larve did not begin to appear under the skin of the 
backs of cattle in that locality for over three months after these 
larvee were taken in the neural canals. 
PREPARATION FOR THE EGRESS OF FULLY DEVELOPED LARVA 
The appearance of third-stage larvee under the skin on the back 
is frequently accompanied by considerable local inflammation, in- 
dicated by edema of the connective tissue and sometimes marked 
swellings and soreness. 
Certain cattle are more prone to such manifestations and show 
swellings as large as 10 inches in diameter around each larva as 
it comes to the subcutaneous tissue of the back. From one to three 
days after the appearance of one of these swellings a minute hole 
is cut by the larva near the center, after which the swelling soon 
subsides. Although no conclusive evidence is at hand, the writers 
are of the opinion that the holes are cut through the skin almost 
