264 LIFE AND HER CHILDREN. 
leaves them to float. In a very short time the eggs 
are hatched and the young grubs swim briskly about, 
whirling round some tufts of hair which grow on 
their mouths, and so driving microscopic animals and 
plants down their throats. Curiously enough they 
Fig. 90. 
Life of a Gnat. 
g, Grub breathing air through the tube /; /, pupa breathing air 
through two tubes t in the back ; b, floating boat formed of the pupa 
skin ; gn t gnat rising out of it ; above the perfect gnat is on the wing. 
These figures are all magnified to give clearness. 
all swim head downwards and tail upwards (g, Fig. 
90), and the secret of this is that they are air-breath- 
ing animals and have a small tube at the end of their 
tail, which they thrust above water to take in air. 
This goes on for about a fortnight, when, after they 
