Page:First course in biology (IA firstcourseinbio00bailrich).pdf/287

 CHAPTER VII

CRUSTACEANS

—In regions where crawfish are not found, a live crab may be used. Locomotion and behavior may be studied by providing a tub of water, or better, a large glass jar such as a broad candy jar. For suggestions on study of internal structure, see p. 58.

Habitat.—Do you often see crawfish, or crayfish, moving about, even in water where they are known to be abundant? What does your answer suggest as to the time when they are probably most active?

Why do you never see one building its chimney, even where crawfish holes are abundant? Is the chimney always of the same color as the surface soil? Are the crawfish holes only of use for protection? In what kind of spots are crawfish holes always dug? Why? What becomes of crawfish when the pond or creek dries up? How deep are the holes? How large are the lumps of mud of which the chimney is built? How does it get them out of the hole? Why is the mud built into a chimney instead of thrown away? (What would happen to a well with its mouth no higher than the ground?) Why are crawfish scarce in rocky regions, as New England?

How does the color of the crawfish compare with its surroundings? Is its color suited to life in clear or muddy water? Define protective coloration.