DIPTEEA. 43 



that the most essential facts in the history of those little creatures 

 would soon be made known to us. "What enjoyment more worthy 

 of the calling they have chosen could these pious men pursue than 

 that which would place before their eyes the marvellous creations 

 of an Almighty Power ? Even their leisure would then incline 

 them to adore that Power, and would furnish them the means to 

 make others do so who are occupied by too serious or too frivolous 

 employments." 



After having changed its skin three times in a fortnight or 

 three weeks, the larva of the gnat throws off its covering for a 

 fourth time; but it is no longer in that state. It is changed 

 both in shape and condition. Instead of being oblong, its body 

 is shortened, rounded, and bent in such a way that the tail is 

 applied to the underneath part of the head. This is the case 

 when the animal is in repose ; but it is able to move and swim, and 

 then, by bending its body and straightening it again, propels 

 itself through the water. 



In this new condition, that is to say, in the pupa state 

 (Fig. 29), it does not eat. It no longer possesses digestive 

 organs, but it is necessary, even more than before its 

 metamorphosis, that it should breathe atmospheric air. 

 Besides, the organs of respiration are greatly changed. 

 During the time the insect was in the larva state, it was 

 through the long tube fixed to the posterior part that it 

 received or expelled the air ; but in casting 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 

 openings of these ears being held above the surface of the 

 water. From this pupa the perfect insect will emerge ; P ^ 2 of 

 it is developed little by little, and the principal members the Gnat- 

 may be distinguished under the transparent membraneous skin 

 which envelops 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 in- 

 creasing very rapidly in length and breadth. 



