FIG. 56. Astacm fluviatilis. The structure of the cuticle. A. trans- 

 verse section of a joint of the forceps ( x 4) ; s, setae ; B, a por- 

 tion of the same ( x 30) ; C, a portion of B more highly magnified, 

 , epiostracum ; b, ectostracum ; c, endostracum ; d, canal of seta ; 

 e, canals filled with air ; s, seta. D, section of an intersternal 

 membrane of the abdomen, the portion to the right in the natural 

 condition, the remainder pulled apart with needles ( x 20) ; E, 

 small portion of the same, highly magnified ; a, intermediate sub- 

 Stance ; &, laminae. F, a seta, highly magnified ; a and b, joints. 



