DIPTEEA. 77 



sary for them to remain on the tainted meat, which has heen 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 Reaumur, " 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 

 a fly. 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 is 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. 



