iqU- Carpenter & Yinvjirr. —History of Warble Flies. 217 
was started again last year (1913), therefore, it was arranged 
to confine all the calves to open ground by means of wooden 
hurdles, so that the muzzled ones should not have the 
indirect protection of shelter. The result in the spring of 
this year was an average of 21 warbles each for ten muzzled 
cattle and 15 each for eleven unmuzzled. Instead of two 
counts only as in previous years, five separate extractions 
of maggots were made at various dates from March 27th 
to June 3rd. At the first two dates the unmuzzled animals 
were quite free from warbles ; at the last count five of the 
muzzled ones were free and two others had but a single 
maggot each. The result of these later experiments tends 
to show, therefore, that muzzling confers no protection 
when the general conditions are similar for both muzzled 
and "control" animals. We cannot yet see why the 
muzzled beasts should be — as they apparently are — attacked 
earlier in the season than the " controls ;" but it seems 
clear that the freedom of the muzzled animals from warbles 
at the late counts in 1910 andi9i2 may be explained by an 
increasing tendency on their part to seek the shade as the 
summer advanced and the weather became hotter. The 
larger proportion of warbles in the unmuzzled animals in 
the especially carefully conducted experiment of 1913-14 
suggests not only that the maggots enter the cattle by boring 
through the skin, and that the normal mode of entrance 
cannot be by the mouth, but that the beast's tongue, 
instead of aiding the maggot in its career, is an important 
factor in reducing the numbers of the parasite. Cattle may 
be observed to lick the place where eggs have been laid, and 
many of the eggs are probably thus knocked off and killed. 
During the last two seasons we have done our best to 
supplement the results of the muzzhng experiments by 
direct observation on the mode of egg-laying and hatching 
of the young maggot. The result of our work in this 
direction during 19 13 has been (by permission of the Depart- 
ment) published in a recent paper^ where we have given 
an account, with figures, of the newly hatched maggot of 
Hypoderma bovis (from eggs that had been kept for four days 
^ Sci. Proc. R. Dublin Soc, vol. xiv., 1914, pp. 268--290, pis. xxi-xxvi. 
