=Habits.=—Does the crayfish walk better in water or out of it? Why? Does it use the legs with the large claws to assist in walking? Do the swimmerets (under the abdomen) move fast or slow? (Observe it from below in a large jar of clear water.) What propels it backward? Forward? Does the crayfish move at a more uniform rate when swimming backward or forward? Why? In which way can it swim more rapidly? Do the big legs with claws offer more resistance to the water while it is swimming backward or forward? How does it hold the tail after the stroke, while it is darting backward through the water? Hold a crayfish with its tail submerged and its head up. Can the tail strike the water with much force? Allow it to grasp a pencil: can it sustain its own weight by its grip? =Feeding.=—Offer several kinds of food to a crayfish that has not been alarmed or teased. Does it prefer bread, meat, or vegetables? How does it get the food to its mouth? Does it eat rapidly or slowly? Does it tear the food with the big pincers? Can it gnaw with the small appendages near the mouth? =Breathing.=—Does the crayfish breathe with gills or lungs? Place a few drops of ink near the base of the hind legs of a crayfish resting quietly in shallow water. Where is the ink drawn in? Where does it come out? To explain the cause and the purpose of this motion, place a crayfish in a large glass jar containing water, and see the vibratory motion of the parts under the front portion of the body. There is under the shell on each side of the body a gill paddle, or gill bailer, that moves at the same rate. =Senses.=—Crayfish are best caught with a piece of meat or beef’s liver tied to a string. Do they always lose hold as soon as they are lifted above the water? What do you conclude as to the alertness of their senses? Does the covering of their bodies suggest the possession of a delicate or a dull sense of touch? Of what motions are the _eyes_ capable? Touch one of the eyes. The result? Can a crayfish see in all directions? To test this, place a crayfish on a table and try whether you can move to a place where you can see the crayfish without seeing its eyes. What are the advantages and disadvantages of having the eyes on stalks? [Illustration: FIG. 81.—CRAWFISH (dorsal surface). ] [Illustration: FIG. 82. ] Touch the body and the several appendages of the crayfish. Where does it seem most sensitive to _touch_? Which can reach farther, the antennæ or the big claws? Why are short feelers needed as well as long ones? Make a loud and sudden noise without jarring the crayfish. Is it affected by _sound_? =External Anatomy= (Figs. 81, 82, 83, 84).—Is the body of the crayfish rounded out (convex) everywhere, or is any part of its surface either flat or rounded in (concave)? What _colour_ has the crayfish? Is this colour of any use to the crawfish? [Illustration: FIG. 83.—LATERAL VIEW OF CRAWFISH. ]