Invertebrates The Crayfish 
making, the doors of which they guard with the big, 
threatening nippers, which stand ready to grapple 
with anybody that comes to inquire if there is any- 
body at home. The upper surface of the crayfish’s 
body is always so nearly the color of the brook bot- 
tom, that the eye seldom detects the creature until 
it moves; and if some enemy surprises one, it swims 
off tail first with terrific jerks which roil all the water 
around and thus cover its retreat. In the winter, our 
brook forms hibernate in the muddy bottoms of their 
summer haunts. There are many species; some in 
our Southern States, when the dry season comes on, 
live in little wells which they dig deep enough to 
reach water. They heap up the soil which they 
excavate around the mouth of the well, making well- 
curbs of mud; these are ordinarily called ‘‘crawfish 
chimnies.’’ The crayfishes find their food in the 
flotsam and jetsam of the pool. They seem fond of 
the flesh of dead fishes and are often trapped by its 
use as bait. 
Looking at the crayfish from below, we see on the 
abdomen some very beautiful featherlike organs 
called swimmerets. Each swimmeret consists of a 
basal segment with twin paddles joined to its tip, 
each paddle being narrow and long and fringed with 
hairs. The mother crayfish has four pairs of these, 
one pair on each of the second, third, fourth and fifth 
segments; her mate has an additional larger pair on 
the first segment. These swimmerets, when at rest, 
lie close to the abdomen and are directed forward and 
slightly inward. When in motion they paddle with a 
backward, rythmic motion, the first pair setting the 
stroke and the other pairs following in succession. 
This motion sends the body forward, and the swim- 
merets are chiefly used to aid the legs in forward 
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