276 THE COMPARATIVE MORPHOLUGY OF THE CRAYFISH. 
are separated from the foregoing by the external maxilli- 
pedes, and lie at the sides of the quadrate space in 
which these organs are set. 
There are only nine gills on each side, and these, 
as in the prawn and shrimp, are phyllobranchia. 
Seven of the branchie are pyramidal in shape, and for 
the most part of large size. When the branchiostegite 
is removed, they are seen lying close against its inner 
walls, their apices converging towards its summit. ‘The 
two hindermost of these gills are pleurobranchie, the 
other five are arthrobranchie. The two remaining gills 
are podobranchie, and belong to the second and the 
third maxillipedes respectively. Each is divided into a 
branchial and an epipoditic portion, the latter having the 
form of a long curved blade. The branchial portion of 
the podobranchia of the second maxillipede is long, and 
lies horizontally under the bases of the four anterior 
arthrobranchis ; while the gill of the podobranchia of 
the third maxillipede is short and triangular, and fits in 
between the bases of the second and the third arthro- 
branchie. The epipodite of the third maxillipede is very 
long, and its base furnishes the valve of the afferent 
aperture of the branchial cavity, which has been men- 
tioned above. The podobranchia of the first maxillipede 
is represented only by a long curved epipoditic blade, 
which can sweep over the outer surface of the gills, and 
doubtless serves to keep them clear of foreign bodies. 
