52 AXIMAL BIOLOGY 



Habits. Does the crawfish 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 crawfish 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 crawfish 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 crawfish 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 crawfish breathe with gills or 

 lungs ? Place a few drops of ink near the base of the hind 

 legs of a crawfish resting quietly in shallow water. Where 

 is the ink drawn in ? Where does it come out ? To ex- 

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

 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 a gill paddle, or gill bailer, under the 

 shell on each side of the body that moves at the same rate. 



Senses. Crawfish 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 



