Fic. 56.—Astacus fluviatilis-The structure of the cuticle. A, trans- 
verse section of a joint of the forceps (x +); s, sete; B, a por- 
tion of the same (x 80); C, a portion of B more highly magnified. 
a, 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); 2, 
small portion of the same, highly magnified ; a, intermediate sub- 
stance ; b, lamine. J, a seta, highly magnified ; a and J, joints. 
