388 DIPTERA. 
the form of the gnat can be perceived 
through the shroud, or case, in which it 
is enveloped, and which is again wrapped 
in an outer case of fine net work. The 
pupae float upon the water, rolled up in 
little spiral balls ; but th^y have the 
power of unrolling, and of diving to the 
bottom, if alarmed. In three or four 
days they burst their case, and, resting 
on it, as on a boat, till they can expand 
their wings, they become at once inhabit- 
ants of the air : but this is a critical mo- 
ment of their existence : should the wind 
be high, and the water agitated, the boat 
fills, and the gnat perishes, 
Lucy. Well, indeed, I should not 
grieve much if they were all to be 
drowned, though they are such curious 
little creatures. I think the plague of 
gnats would be as vexatious as the plague 
of locusts. 
Mother, But not quite so destructive. 
The proboscis, or trunk, is the most 
wonderful part of the gnat ; it is com- 
posed of an outer tube, which is so flexi- 
