496 
Observations on the Development of Ox Warble, 
skin, and thus was enabled to secure the specimen whilst still 
bearing the rejected early form of spiracles in the old skin, with 
their lower ends still attached to the new kidney-shaped pair 
now formed at the tail of the ma^ffot. 
Figs. 10 and 11 show the old club-shaped form, resting on the 
Fig. 10. — Early form of 
Spiracle, with fragment 
of Moulted Skin, still 
attaclied to Kidney-form 
sTiape, much macjntfied. 
Fig. 11— Ficj. 10 in 
different position, show- 
ing Breathing Pores. 
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 thick- 
ness 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 magnified at Fig. 9. These are the termina- 
tions of cylindrical passages which are connected lower down, 
and which appear, as far as the thickness of the chitinous 
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 
branchlets 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. 12 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 
