224 



THE CRAYFISH 



slight degree by two still smaller paired maxillae just under the maxil- 

 lipeds. Ultimately the food reaches the hard jaws and, after being ground 

 between them, is passed down to the stomach. 



Breathing. — The mouth parts of a crayfish resting ia the aquarium 

 are observed to be constantly in motion, despite the fact that no food 

 is present. If a crayfish is taken out of the water and held with the 

 ventral surface upmost, a little carmine (dissolved in water) may be 

 dropped on the lower surface and allowed to run down under the cara- 

 pace. If now the animal is held in water in the same position, the carmine 

 will reappear just beyond from both sides of the mouth, seemingly pro- 

 pelled by something which causes it to emerge in Httle puffs. If we 



Some appendage3 of the crayfish: 1, the jaw, with palp; 2, first maxilla (second 

 maxilla not shown): 5, third maxillipod ; 4, second maxilUped, showing baler; 

 5, first maxilUped, showing gill attached ; 6, walking appendage, showing attach- 

 ment of gill ; 7, swimmeret ; 8, uropod. 



remove the maxillipeds and maxillse from a dead specimen, we find a 

 groove leading back from each side of the mouth to a cavity of con- 

 siderable size on each side of the body under the carapace. This is the 

 gill chamber. It contains the gills, the organs which take oxygen out 

 of the water. The second maxillse are prolonged down into the groove 

 to serve as bailers or scoops. By rapid action of this organ a current 

 of water is maintained which passes over the gills. 



The gills are outside of the body, although protected by the carapace. 

 If the carapace is partly removed on one side, they will be found looking 

 somewhat like white feathers. The blood of the crayfish passes by a 

 series of vessels into the long axis of the gill ; in this organ the blood 

 tubes divide into very minute tubes, the walls of which are extremely 



