47 
of the maggot. The hard “ tips,” serviceable for forcing a passage 
up the hide, are no longer needed, and they are exchanged for a 
broader form; they are cast entirely with the moulted skin, and in 
the newly exposed surfaces beneath we find the first appearance of 
the well-known kidney-shaped spiracles (figured at p. 46, magnified), 
which are what are to be seen as two little black dots at the tail- 
end of the maggot in the open warble. * 
The changes of condition appeared to be rapidly gone through, 
and it was when the maggot had gained about a quarter or third of 
its growth that the spiracles were developed to their angularly 
kidney-shaped form, and the maggot assumed the compressed oval 
shape in which it is best known. It was still white, but opaque, 
and with the segments well marked; and the early part of its work 
being done, and the warble-passage open, it has no occasion now to 
bore its way , and ceases to be furnished with a form fitted for perforation. 
Other alterations of a very practical bearing also take place at 
this time, or follow on this most important of the moults. The 
Muscles within skin of maggot, and prickles outside skin of maggot, 
much magnified. 
skin of the maggot becomes furnished within with a powerful coat 
of muscles (see figure), extending over it like basket-work, which 
give it a power of contraction and expansion. Externally in this 
stage the skin of the maggot is furnished with a much larger 
amount of prickles arranged in more numerous bands, than are 
noticeable in the previous stages. The prickles are now strong 
enough to cause an unpleasant sensation when the maggot crosses 
* In my own observations I was fortunate enough to see a maggot in the 
very act of moulting off its first form of spiracles, and to be able to secure the 
specimen, which I still preserve for microscopic use, and also had carefully 
figured, showing the early as well as the adult form not quite completely 
separated. 
