20 
presence of any distinct lining membrane. With the enlarge¬ 
ment of the passage, its shape became more cone-like, corres¬ 
ponding with the altered form of the maggot; and on March 
5th she found for the first time a distinct skin-like membrane, 
covering the walls of the perforation or passage, and con¬ 
tinuous with the lining of the maggot cell below. The 
amount of development of the warbles at a given date varied * 
very much ; warbles just beginning to form might be found 
together with those nearly three-quarters of an inch across, as 
measured on the fleshy side of fresh hide on the 4th of March ; 
but, when once started in growth, the progress was very 
rapid. 
The great change, both in the appearance and the internal 
structure of the maggot, took place when it was grown to 
about one-third of its full size, when it assumed its well- 
known shape. Previously to this, its chief characteristics, 
externally, were the absence of anything that could obstruct 
its power of pressing onwards; and internally it was little « 
more than a bag of fluid, with a large proportion of the space 
occupied by breathing tubes—a very important consideration * 
relatively to available methods of destroying the creature. V 
At the period, however, of its moult to its final stage, a change 
takes place respectively in the nature, or in the amount of 
development of nearly the whole of both the internal and 
external structure of the maggot. The hard tips are now no 
longer necessary for forcing a passage, and they are exchanged 
for a broad form of spiracle, and the internal organs become 
suited to provide material for the development of the fly, 
which will presently form in the dry husk of the maggot 
which serves as the chrysalis case. One of the first and most 
remarkable of these changes is the complete alteration in the 
form of the spiracles. Up to this stage the general form 
continued to be that of a pair of short, horny, somewhat bent, 
cylindrical, or partially cylindrical tubes, covered at the end 
(fig. 10) with round or oval discs, which appear to have a 
definite narrow border, and across the centre of the disc to be 
of a sieve-like or spotted appearance. These discs may 
amount to as many as twenty-six on each spiracle, and 
appeared to her to be placed each at the extremity of short 
cylinders. The structure is most elaborate and peculiar. * 
r 
