firmly fixed in the head; they cannot move about as do ours. 
But to aid the fly in seeing objects in all possible directions, 
we find by a minute study that the eyes which occupy such 
prominent positions on the head are really two great bundles 
of small eyes, so small that they can only be detected with 
a magnifying glass. It has been estimated that each of these 
two bundles of eyes is made up of 4,000 simple eyes, which 
radiate from a common center like the bristles in a paint¬ 
brush. One might think that with 8,000 eyes so much more 
is seen by a fly than by a man, with only two eyes. But it 
must be true that the eyes of a fly are exceedingly simple in 
structure, and therefore limited in power of vision. 
Let us next observe the wings of the fly. It has only two 
wings. But why should we say only two wings ? Because we 
see that nearly all other insects have four wings. This is 
true of the butterflies and beetles, the dragon - flies and 
bumblebees. Therefore, we should be surprised to find only 
two wings on the fly. All true flies have but two wings. 
Nature is so faithful to her “types” of animals and plants 
that when we find a typical part wanting, we search for a 
rudiment or concealed mark of the place where the missing 
part belonged. Then let us search the fly for the mark of 
the missing pair of wings. If we remove one wing we will 
see a light-colored membrane protruding from the body of 
the fly. This might be mistaken for a rudimentary wing; but 
it is not the part we are searching for, since it does not 
occupy the right place for the rear wing. Remove this mem¬ 
brane-like appendage (which is greatly developed in the house¬ 
fly, and is called the alulet), and we may see a delicate hair 
with a whitish knob on the end. This hair is attached to 
the body of the fly at the point where the rear wing would 
be, if present; another may be seen in the corresponding 
place on the other side of the fly. Such hairs, terminated 
with knobs, are present in other two-winged flies, and are 
more easily seen in the crane-fly (see cut), which we often 
see walking over our windows, looking like giant mosquitos. 
These hairs are called “balancers,” or “poisers,” or halters, 
because it is supposed that they aid the flies to poise “on 
the wing.” 
The house-flies &re very common about barns in August 
and September. The reason for this is that they lay their 
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