17 
to form a case for the developing Fly within. But it 
differs a little in form from the maggot in being almost 
flat below. 
Chrysalis of Ox Warble Fly, side view, and shewing contained Fly. 
The chrysalis state lasts in common circumstances 
from twenty to thirty days, but is very much lengthened 
by cold weather, especially severe night-chills. 
If we look now for the main points of the history of 
the Ox Warble Fly, which are to be considered regarding 
methods of prevention or remedy, we find the follow¬ 
ing : 
1. The egg is laid on or in the cattle. We need to 
find how to secure, or allow the cattle to secure them¬ 
selves from having the eggs laid on them; and also 
whether there is any method of treatment by which 
the egg, if laid, can he removed, or the young grub 
killed. 
2. When the maggot has established itself in the 
hide, how early in its life, and by what measures we may 
most certainly and easily destroy it at a paying rate, 
without doubt as to the soundness of the work, or pain 
or risk to the cattle. 
8. Considerations as to what changes occur in the 
surface of the warble-cell, relatively to the importance 
pecuniarily of getting rid of the maggot before the new 
skin forms over most of the surface of the cavity, which 
prevents subsequent healing taking place. 
On some of these points we have gained information 
from experiments made this year, and on some we may 
gather much of which we need by comparing published 
and contributed observations, amongst them some very 
B 
