40 THE INSECT WORLD. 



its skin it loses the tube, two appendages resembling an ass's ears 

 being for the pupa what the tube was for the larva, the opening of 

 these ears being held above the surface of the water. From this 

 pupa the perfect insect will emerge ; it is developed little by little, 

 and the principal members may be distinguished under the transparent 

 membranous skin which envelopes it. 



When the insect is about to change from the pupa state, it lies on 

 the surface of the water, straightening the hind part of its body, and 

 extending itself on the surface of the water, above which the thorax 

 is raised. Before it has been a moment in this position, its skin 

 splits between the two breathing trumpets, the split increasing very 

 rapidly in length and breadth. 



" It leaves uncovered," says Re'aumur, " 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. 



" As soon as the split 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 forward 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 



