10 
WARBLE ELY. 
The above are the main differences connected with the moult to the 
final form of the maggot, and, following on these alterations in its 
structure, and especially on the power of keeping up a constant irrita¬ 
tion by means of the muscular expansion and contraction of its 
prickly skin, we find the lining membrane of the cell increasing in 
thickness, until it becomes well defined as a tough wall round the 
perforation, continuous with the upper part of the cell. Fig. 12 
shows a cell drawn in section, and slightly magnified after maceration 
in water. The lowest end of the maggot-chamber appears full of foul 
matter, caused by the irritation of the friction and suction of the 
Fig. 12. Fig. 13. 
Fig. 12. — Warble-cell, slightly larger than life. Fig. 13. — Chrysalis of Ox Warble 
Fly, side view, and showing contained fly. 
maggot; and, after the creature has crawled from its hole, a pressure 
on the empty warble is followed by a discharge of some amount of 
purulent matter. 
When the warble-maggot is full-fed it presses itself gradually out 
of the opening at the top of the warble, which at first sight looks much 
too small for the exit, but the opening can be squeezed somewhat 
larger, the soft maggot is compressible, and is further helped in 
dragging itself out by the ringed shape and roughened skin, which 
prevent its slipping back again into its former hole. When it has 
fallen to the ground it creeps to some shelter, under a stone, a clod, 
or where may be convenient, and there the skin hardens into a chrysalis 
coat much like the grub, excepting in being dark brown or blackish in 
colour, and somewhat flattened on one side (see fig. 13). From these 
chrysalids the Warble Flies come out, in favourable weather, in about 
four weeks from the dropping of the maggot from the back of the 
cattle ; in cold weather the time required for the change is longer.* 
When the maggot has gained the condition mentioned above it 
undergoes no further great change until it turns to the chrysalis-state. 
The spiracles become less radiated and darker, the maggot also 
becomes darker as it increases in size; but the main points of its life 
now are to form, at the expense of the animal in which it lives, the 
material from which the fly will presently be developed. 
* For details see ‘ Essay on Bots,’ by Bracy Clark ; * Monographie der CEstriden,* 
by Friedrich Brauer and other writers. 
