ANATOMY AND PHYSIOLOGY. _ 117 
falling. Wasps cannot soar, and their wings are 
never tranquilly extended in the air, but the form 
and position of their bodies are as important elements 
in their flight as in that of the sea-gull, and, however 
disguised or complicated, the principles which sustain 
and direct them are the same as those which sustain 
and direct the kite or the ball. 
In such little creatures we cannot take exact 
measures of all the curves of their surfaces. But we 
may safely assume that their lines, as a ship-builder 
would call them, are as accurately adapted to their 
physical requirements as is the rest of their structure. 
Designed always to sail on a cross wind, they are 
doubtless formed so as to sail as near the wind and 
make as little lee-way as any vessel. In other words 
designed to fly horizontally, under a downward 
pressure, they are doubtless formed so as to fall as 
little, and to advance as much, as possible. 
Then, as to position. A bird falls when it is 
winged, and a ship, unless her sails be drawn to the 
right angle, and her head be kept straight in her 
course, is no better than a log on the water. We 
cannot watch these little atoms very closely as they 
flit by us, but we can learn from the examination of 
their bodies, that they have means, as effectual as a 
ship’s rudder, for keeping their course. Bearing in 
mind that the pressure on an insect is obliquely verti- 
eal, not obliquely horizontal, as in a ship, we shall see 
that: everything has been most amply provided for. 
A wasp can raise or depress her abdomen at will, and 
so alter the angle at which she lies on the air; she 
can trim her balance from side to side by means of 
her air-sacs; and she can adjust her wings, as exactly 
