44 THE INSECT WOELD. 



" It leaves," says Reaumur, " a portion of the thorax of the 

 gnat, easily to be recognised by the freshness of its colour, which 

 is green, and different from the skin in which it was before 

 enveloped, uncovered. 



" As soon as the slit is enlarged and to do so sufficiently is 

 the work of a moment the fore part of the perfect insect is not 

 long in showing itself; and soon afterwards the head appears, 

 rising above the edges of the opening. But this moment, and 

 those which follow, until the gnat has entirely left its covering, 

 are most critical, and when it is exposed to fearful danger. This 

 insect, which lately lived in the water, is suddenly in a position 

 in which it has nothing to fear so much as water. If it were 

 upset on the water, and the water were to touch its thorax or body, 

 it would be fatal. This is the way in which it acts in this critical 

 position. As soon as it has got out its head and thorax it lifts 

 them as high as it is able above the opening through which they 

 had emerged, and then draws the posterior part of its body 

 through the same opening ; or rather, that part pushes itself for- 

 ward by contracting a little and then lengthening again, the 

 roughness of the covering from which it desires to extricate itself 

 serving as an assistance. 



"A larger portion of the gnat is thus uncovered, and at the 

 same time the head is advanced farther towards the anterior end 

 of the covering ; but as it advances in this direction, it rises 

 more and more, the anterior and posterior ends of the sheath thus 

 becoming quite empty. The sheath then becomes a sort of boat, 

 into which the water does not enter; and it would be fatal 

 if it did. The water could not find a passage to the farther 

 end, and the edges of the anterior end could not be submerged 

 until the other was considerably sunk. The gnat itself is the 

 mast of its little boat. Large boats, which pass under bridges, 

 have masts which can be lowered ; as soon as the boat has passed 

 the bridge, the mast is hoisted up by degrees, until it is perpen- 

 dicular. The gnat rises thus until it becomes the mast of its own 

 little boat, and a vertical mast also. It is difficult to imagine how 

 it is able to put itself in such a singular, though for it necessary, 

 position, and also how it can keep it. The fore part of the boat is 

 much more loaded than the other, but it is also much broader. 



