WARBLE FLY. 
105 
Figs. 9 and 10 show the old club-shaped form, resting on the 
kidney-shaped form, which, after this change, lasts, with some slight 
modification, through the rest of the life of the maggot. 
The newly-formed spiracle, having had a portion of its thickness 
removed so as to show it as a transparent object, will be observed to 
be furnished at the upper surface with numerous cylindrical pores or 
openings, corresponding in appearance with those represented magni¬ 
fied at fig. 8. These are the terminations of cylindrical passages 
which are connected lower down, and which appear, as far as the 
thickness of the cliitinous material allows them to be traced, to be 
ramifications of a small number of upright passages opening from the 
great trachea below, and passing upward through the spiracle, thus 
giving communication with the outer air by means of the cylindrical 
branclilets with their open extremities. 
The internal apparatus of the spiracles and the attached breathing- 
tubes underwent a corresponding change at the time of this moult. 
Fig. 11 gives an inside view of the base of the newly-formed spiracles 
with apertures in the centre, leading into the old pair above them. 
The parallel lines round a portion of the circumference of the 
fluted saucer-like discs, and the raised portion round the central 
perforation, show where a small portion of the old and new air-tubes 
(tracheae), belonging to the old and new spiracles, were cut through 
in making the transverse section. 
These air-tubes, like the spiracles at their extremities, were now, 
at this portion of the maggot, in duplicate. This in itself is not 
remarkable, but it is not often that the moult of the tracheae can be so 
perfectly observed. A reference to fig. 5 will show the general 
appearance of the tracheae of the maggot, with the cross trachea that 
Fig. 11. Fig. 12. 
Fig. 11.—Bases of pair of old and new spiracles (viewed vertically), much 
magnified. Fig. 12.—Section of tracheae, much magnified. 
joins the two main tubes ; and, on making a section across at this 
point, the old air-tube with its branch was clearly to be seen, lying 
detached in the corresponding part of the new tube. 
The cross section shown at fig. 12 shows the newly-formed trachea 
with the connecting tunnel, and within one of the tubes is a section 
of the smaller old trachea, now floated loose in the balsam in which 
