the mercy of birds, fish, and other enemies while in this soft and defenseless condition, it stays hidden until the covering hardens. Hence it cannot eat much, but probably by the absorption of water the tissues grow; that is, enlarge. In the intervening periods, when growth is impossible, it develops; that is, the tissues and organs change in structure and become stronger. "Soft-shelled crab" is a popular dish, but there is no species by that name, this being only a crab just after molting which has been found by fishermen in spite of its hiding.
General Questions.—How do crawfish choose their food?
How long can they live out of water? Why do their gills remain
moist out of water longer than a fish? How do they breathe
out of water? Are they courageous or cowardly animals? When
they lose appendages when fighting or molting, they are readily
reproduced, but the part molts several times in regaining its
size. Have you seen crawfish with one claw smaller than the
other? Explain.
Compare the crawfish and crab (Figs. 81, 93, and 95) in the following particulars: shape, body, eyes, legs, abdomen, habitat, movement.
KEY TO THE FOUR CLASSES IN BRANCH ARTHROPODS
1. Insects 3 body divisions, 6 legs
2. Arachnids 2 body divisions, 8 legs
3. Myriapods many body divisions, many legs
4. Crustaceans gill breathers, skeleton (external) limy
By the aid of the key and of figures 96-105, classify the following
Arthropods: tick, thousand-leg centipede, king crab, pill bug, spider,
scorpion, beetle.
