THE INSECT WOELD. 



The fly always comes out at the same end of the cocoon, that is, 

 at the end where its head is placed, and also where the head of the 

 larva previously was. This end is composed of two parts of two 

 half cups placed one against the other. These can be detached 

 from each other and from the rest of the cocoon. It is sufficient 

 for the fly that one be detached, and in order to effect this, it 

 employs a most astonishing means. It expands and contracts its 

 head alternately, as if by dilatation ; and thus pushes the two half 

 cups away from the end of the cocoon. These are not long able 

 to resist the battering of the fly's head, and the insect at length 

 comes out triumphant. This fly, which should be blue, is then 

 grey; it, however, comes quickly to perfection, at the end of 

 three hours attaining its definite colour ; and in a very short 

 space of time every part of the animal becomes of that firmness 

 and consistency which characterise it. At the same time, the 

 wings, which at the moment it came into the world were only 

 stumps, extend and unfold themselves by degrees. The meat-fly 

 is represented below (Fig. 55). 



One of the features in the formation of this fly which most 



attracted the attention of 

 Reaumur, and which is likely 

 to excite the curiosity of all 

 those who take an interest in 

 insects, is the composition of 

 its trunk. We will therefore, 

 with that illustrious observer, 

 take a glimpse at the remark- 

 able and complicated appa- 

 ratus by the aid of which the 

 fly can suck up liquids, and can even taste solid and crystalline 

 substances, such as sugar. 



It is no difficult matter to make a fly show its trunk, 

 extended to its full extent. One has only to press between 

 the finger and thumb either the two sides or the upper and under 

 part of the thorax. It is thus forced at once to put out its 

 tongue. 



The tongue appears to be composed of two parts joined together, 



Fig. 55. Blue-bottle fly 

 ( CaUipkora vomitoria) magnified. 



