362 



THE CRAYFISH 



CHAP. 



as to have the character of a hard, jointed armour. Tufts of 

 minute feather-like cuticular structures, or seta, are present 

 on various parts of the exoskeleton both of the body and 

 appendages. 



It has been stated that the abdominal segments are 

 movable upon one another in a vertical plane : i.e., the whole 



EM, 



FIG. go. Transverse section of abdomen of Crayfish. 



DA. dorsal abdominal artery ; EM. dorsal muscles of the abdomen ; EP. space 

 between the pleuron and the appendage ; FM. ventral muscles of the abdomen ; 

 M. muscles of the appendage ; N. endopodite ; NG. nerve-ganglion ; P. protopodite ; 

 PL. pleuron ; PR. hind-gut ; S. sternum ; T. tergum ; V. ventral abdominal artery ; 

 X. exopodite. (From Marshall and Hurst's Zoology). 



abdomen can be extended or straightened, and flexed or bent 

 under the cephalothorax ; the segments are incapable of 

 movement from side to side. This is due to the fact that, 

 while adjacent segments are connected dorsally and ven- 

 trally by flexible articular membranes, they present at each 

 side a joint, placed at the junction of the tergum .and 



