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?
Fig. 81.—Crawfish (dorsal surface).
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?
