286 STATES OF INSECTS. (Pupa.) 
The gnat has to undergo its change on the surface of 
the water.—How is it to accomplish this without being 
wetted? In the pupa state they usually remain sus- 
pended with the posterior end of the body turned down- 
wards: but when the period for its change is arrived, it 
stretches it out upon the surface, above which its thorax 
is elevated. Scarcely has it been a moment in this po- 
sition, than, swelling out the interior and anterior parts 
of the thorax, it causes it to split between the two respi- 
ratory horns. Through this opening the anterior part 
of the gnat then emerges. As soon as the head and 
trunk are disengaged, it proceeds with its labour, and 
gets out more and more; elevating itself so as to appear 
in the puparium like a mast in a boat. As it proceeds, 
the mast is more and more elevated and lengthened, till 
it becomes nearly perpendicular—just as the mast of a 
boat is gradually raised from a nearly horizontal to a 
vertical position: at this period a very small portion of 
the abdomen remains in the puparium. Neither its legs 
nor wings are of any use in maintaining it in this posi- 
tion. The latter are too soft, and, as it were, folded; 
and the former are stretched out along the abdomen— 
the segments of this last part are the only agents. The 
observer who sees how the little boat gradually sinks, 
and how its margin approaches the water, forgets the 
mischievous insect it contains, which at another time he 
would crush without remorse, and becomes interested 
for its fate; especially should wind agitate the water. A 
very little is sufficient to drive about rapidly the little 
voyager, since it catches the wind in some degree as a 
sail. If it should be upset, it would be all over with it; 
—and numbers do thus perish. The gnat, after having 
