264 THE COMPARATIVE MORPHOLOGY OF THE CRAYFISH. 
and when this number is present, the total is made up 
of the same numbers of podobranchie, arthrobran- 
chiez, and pleurobranchie attached to corresponding 
somites. In Palinurus and in the genus Astacopsis 
(which is one of the Parastacide), for example, there are 
six podobranchie attached to the thoracic limbs from 
the second to the seventh inclusively; five pairs of arthro- 
branchie are attached to the interarticular membranes 
of the thoracic limbs from the third to the seventh 
inclusively, and one to that of the second, making eleven 
in all; while four pleurobranchie are fixed to the 
epimera of the four hindmost thoracic somites. More- 
over, in Astacopsis, the epipodite of the first thoracic 
appendage (the first maxillipede) bears branchial fila- 
ments, and is a sort of reduced gill. 
These facts may be stated in a tabular form as 
follows :— 
The branchial formula of Astacopsis. 
Somites and Arthrobranchie. 
their Podo- —+ Pleuro- 
Appendages. branchie. Anterior. Posterior. branchie. 
VII. ... O(ep.x. 0 0 0 = = Ocep.r.) 
VIII, 1 7 1 0 0 = 2 
Ix, 1 1 1 0 = 38 
x. 1 1 i 0 = 8 
XI. 1 i bi x = st 
XII. 1 1 1 1 Se ad: 
- XII, 1 1 1 i — ee 
XIV. 0 0 0 1 = 1 
6+eprn + 6 + 5 + 4 = 21+ep.r, 
