106 
WARBLE FLY. 
it is preserved, but which, when freshly cut, had its main side-branch 
down the side-branch of the larger tube. 
These special observations on the moult of the breathing- 
apparatus may very possibly not bear practically on the subject of the 
prevention of warble injury ; but they are of interest to show how 
minutely we are acquainted with the history of this maggot, the 
ravages of which are, in many cases to this day, left unchecked, as 
being a pest of unknown nature, and of which therefore the cure is 
unknown ; and, further, the specimens give an unusually detailed 
example of the completeness of this internal moult. The sections 
having been taken so as to remove respectively some small fragments, 
both of the brown and the white structure at the junction of the 
spiracles with the tracheae, they may be accurately fitted together 
again, and thus form a whole, showing the old spiracle still bearing 
the old skin round its top raised on the new form, likewise surrounded 
by the new skin ; and beneath we have the corresponding old and new 
air-tubes. 
Other alterations of a very practical kind also take place at this 
time, or follow on this most important of the moults. The skin of 
the maggot becomes furnished within with a powerful coat of muscles, 
extending over it like basket-work. A maggot at this stage, besides 
the power of contraction and expansion, which may be observed in 
protruding and withdrawing the mouth-end with the regularity of 
pulsation, has a power of dragging itself along at a rate of three times 
its own length in two minutes, and has a very definite method of 
progression. The mouth-end is somewhat raised, and the creature 
Fig. 13. 
Fig. 14. 
Fig. 13. —Muscles within skin of maggot, magnified. Fig. 14.—Prickles of 
maggots, much magnified. 
appears to move with as settled a purpose in any given direction as 
other grubs or caterpillars. Externally, in this stage the skin of the 
maggot is furnished with a much larger amount of prickles, arranged 
