104 
WARBLE FLY. 
series of cylindrical projections about twenty in number. With a very 
high power of the microscope the distal end of each of these projections 
appears to be sieve-like, an arrangement which, doubtless, prevents 
the entrance of any foreign matter into the respiratory system.” 
Whether in the case of the warble-maggot the spotted or sieve-like 
appearance is given by microscopic hairs placed to preserve the 
entrance free, or by other structures, I could not ascertain on account 
of the excessive minuteness of the organs ; but a fringe of this nature 
is to be found in some forms of spiracle, and the use of such an 
apparatus to guard the entrance of breatliing-tubes, when acting in a 
passage which is being formed in living hide, is obvious. 
Up to the time when the moult takes place to the final form of 
which I am now speaking, these spiracles are buried up to their disc- 
covered tips in the tail-end of the maggot ; but then they are cast off 
entirely with the moulted skin, and in the newly-exposed skin beneath 
* we find the first appearance of spiracles of the well-known kidney 
shape, but with the surface more radiated, and of a paler chestnut- 
colour than in their later condition. 
During the spring investigations I had an opportunity more than 
once of observing, and also securing, both the moulted skin containing 
the early form of spiracle, and likewise the proprietor maggot, bearing 
the new kidney-shaped pair; and also, in one instance, secured the 
Fig. 9. Fig. 10. 
Fig. 9— Early form of spiracle, with fragment of moulted skin, still attached to 
Kidney-form shape, much magnified. Fig. 10.—Fig. 9 in different position, 
showing breathing-pores. 
maggot when about to moult off the old 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 maggot. 
