118 
WARBLE FLY. 
ends, or end (according to age), adapted them most perfectly, in the 
first stage, for “travelling,” in the second for pushing themselves up 
small end foremost, armed with the minute hard spiracles, through 
the opening warble. 
As far as I see at present the changes of condition I have mentioned 
above are rapidly gone through, and, when the maggot has gained 
about a quarter or third of its growth, the spiracles are developed to 
an angularly kidney-shaped form, and the maggot assumes the com¬ 
pressed oval shape in which it is best known. It is still white, but 
opaque, and with the segments well-marked ; it has no occasion now to 
bore its way, and ceases to be furnished with a form fitted for perforation. 
On placing the very young maggots in water they swell so much as 
to become exceedingly rigid, and so transparent that much of the 
internal structure could be plainly seen. 
By microscopic investigation the spiracles—that is, the blackish 
kidney-shaped spots which are seen at the tip of the maggot in the 
open warble—have two, and I think three, different successive forms 
before developing to the final and best known state ; and they also 
differ from each other in the amount of spiracle exposed at the tip of 
the grub. 
The breathing apparatus consists of a trachea, or breathing-tube 
from each of these spiracles or breathing-pores, and from each trachea 
a series of lesser and lesser tubes carries the air through the maggot. 
The two principal tracheae are tied together near the spiracles by 
another short one, which forms a kind of bridge, or rather tunnel, of 
communication, and thus insures air supplies being continued if one 
spiracle should be choked. I also find that the young maggot 
possesses (apparently as an instrument for tearing out food) a pair of 
crescent-shaped forks or diggers. These are of such excessive 
minuteness that they are only to be found with difficulty, and I have 
not as yet found them in any but very young maggots. A fairly high 
magnifying power is needed for distinguishing their shapes; in my 
own case I have used a quarter-inch glass. 
The difference in appearance, and especially in their glass-smooth 
rigidity, is so great between the young maggots when alive and fully 
inflated, and after death, when their flaccid condition conveys no idea 
of what their piercing powers have been, that I submit the above 
observations as being not merely of scientific curiosity, and hope to 
complete the investigation, and offer it in due time with illustrative 
figures. The above points seem to me to throw light on the probable 
method of formation of the opening of the warble through the hide. 
I do not find this passage (in great contrast to what is below) to be 
ulcerated or torn ; it is merely a clean passage through the hide, 
smooth and shiny, as might be expected to be made by the pressure of 
