266 THE COMPARATIVE MORPHOLOGY OF THE CRAYFISH. 



The hranchial formula of Astacus, 



G + cp. ■»- 6 +5 + 1 h2or3r= 18 + ep. + 2or3r. 



In Camharns, the number of the branchise is reduced 

 to seventeen by the disappearance of the last pleuro- 

 branchia ; while, in Astacoides, the process of reduction 

 is carried so far, that only twelve complete branchise are 

 left, the rest being either represented by mere rudiments, 

 or disappearing altogether. 



The branchial formula of Astacoides. 



XIV. ... 







1 = 



6 + €2^. r 5 + r + + 4 r -f 1 = 12 + ep. r. + 5 r. 



