

DIPTERA. 77 
sary for them to remain on the tainted meat, which has been alike 
their cradle and their larder, and where until now they were so 
well off. They therefore leave it and seek a retreat under ground. 
The larva then assumes a globular form and reddish colour, loses 
all motion, and cannot any longer either lengthen or shorten, or 
dilate or contract itself. Life seems to have left it. ‘It would be 
considered a miracle,” says Réaumur, “if we were told there was 
any kind of quadruped of the size of a bear, or of an ox, which at 
a certain time of the year, the beginning of winter for instance, 
disengages itself completely from its skin, of which it makes a box 
of an oval form; that it shuts itself up in this box; that it knows 
how to close it in every part, and besides that it knows how 
to strengthen it in such a manner as to preserve itself from the 
effects of the air and the attacks of other animals. This pro- 
digy is presented to us, on a small scale, in the metamorphosis 
of our larva. It casts its skin to make itself a strong and well- 
' closed dwelling.”’ 
If one opens these cocoons only twenty-four hours after the 
metamorphoses of the worms, no vestige of those parts appertaining 
to a pupa is to be found. But four or five days afterwards, the 
cocoon is occupied by a white pupa, provided with all the parts of 
_afly. The legs and wings, although enclosed in sheaths, are very 
distinct ; these sheaths being so thin that they do not conceal 
' them. The trunk of the fly rests on the thorax ; one can discern 
| its lips and the case which encloses the lancet. The head is large 
and well formed, its large, compound eyes being very distinct. 
The wings appear still unformed, because they are folded, and, as 
| it were, packed up. It is a fly, but an immovable and inanimate 
fly ; it is like a mummy enveloped in its cloths. 
Nevertheless, it is intended this mummy should awake, and 
when the time comes it will be strong and vigorous. Indeed it has 
need of strength and vigour to accomplish the important work of 
its life. Although its coverings are thin, it is a considerable work 
for the insect to emerge, for each of its exterior parts 1s enclosed 
in them as in a case, much the same as a glove fits tightly to all 
the fingers of the hand. But that for which the most strength is 
necessary is the operation of forming the opening of the cocoon, in 
which as a mummy it is so tightly enclosed. 


