362 



THE CRAYFISH 



CHAP. 



fied so as to have the character of a hard, jointed 

 armour. Tufts of minute feather-like cuticular struc- 

 tures, or setce, are present on various parts of the exo- 

 skeleton 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 



EM 



PL- 



FIG. 90. Transverse section of abdomen of Crayfish. (.X 4.) 

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

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

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

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

 abdominal artery ; X. exopodite. (From Marshall and Hurst's Zoology.} 



whole 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 con- 

 nected dorsal ly and ventrally by flexible articular 

 membranes, they present at each side a joint, placed at 



