INSECT SIPPERS AND GNA WERS. 265 
have changed their skins three times, they are ready 
to remodel their bodies. Then on casting their 
skin for the fourth time they come out shorter and 
bent and swathed up, but still able to swim about 
though not to eat. Meanwhile a most curious change 
has taken place. The tail tube has gone, and two 
little tubes (p t> Fig. 90) have grown on the top of the 
back, and through them the tiny pupa now draws in its 
breath as it wanders along. At last the time comes 
for the gnat to come forth, and the pupa stretches 
itself out near the top of the water, with its shoulders 
a little raised out of it. Then the skin begins to split, 
and the true head of the gnat appears and gradually 
rises, drawing up the body out of its case. This is a 
moment of extreme danger, for if the boat-like skin 
were to tip over it would carry the gnat with it, — 
and in this way hundreds are drowned — but if the 
gnat can draw out its legs in safety the danger is 
over. Leaning down to the w r ater he rests his tiny 
feet upon it, unfolds and dries his beautiful scale- 
covered wings, and flies away in safety. 
With the gnat we must take our leave of the two- 
winged flies, although if we could study their whole 
history we should find them so intelligent that we 
should not be surprised at Mr. Lowne's statement 
that, although a fly is not one-fourth the size of a 
beetle, its brain is thirty times larger. In fact it is 
among these creatures which undergo metamorphosis 
that we begin to reach a point of intelligence which, 
of its kind, is quite as remarkable as that of the back- 
boned animals. But it is not among the butterflies, 
beetles, or even the two-winged flies, that the highest 
instincts are found. There exists an immense ordei 
