52 BEGINNERS' ZOOLOGY 



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 ab- 

 domen) 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 ex- 

 plain the cause and the purpose of this motion, place a cray- 

 fish 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 



