232 
NATURE’S CRAFTSMEN 
a pump when one draws out the piston, promptly 
fills with air, and presto! the worm is able to float 
about to suit his pleasure. The air in the stern, 
you see, buoys up the little craft, just as the air 
in a life-preserver holds a person up in the water. 
If an enemy approaches, or if for any reason 
whatever the worm wishes to go below, all he 
needs to do is to draw in his body, thus expelling 
the air, when his little submarine sinks instantly. 
Progress downward is controlled by the action of 
the occupant: he can stop any time he pleases 
simply by thrusting his body forward and out, 
thus taking on a ballast of air.” 
“ Seems to me the caddis worm should be rea¬ 
sonably safe from enemies,” Alice commented 
musingly. “ Few creatures, I imagine, would 
think of swallowing a bunch of floating sticks or 
pebbles! ” 
“ You forget that the eyes of the water crea¬ 
tures are sharper than ours in some respects,” 
smiled Uncle John. “ They know the caddis 
worm’s habits, and not a few of them are always 
on the alert to catch him unawares. Wait! I be¬ 
lieve we can have some good sport,” and Uncle 
John in his turn stooped and brought up a little 
caddis boat. Then he beckoned silently and 
moved quietly alongshore until he reached a fair¬ 
sized rock which jutted out into the water. From 
this broad vantage point a group of shiny black 
