276 THE COMPARATIVE MOEPHOLOGy OF THE CRAYFISH. 



are separated from the foregoing by the external maxiUi- 

 pedeB, 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 phyUohranchise. 

 Seven of the branchiae 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 pleurobranchise, the 

 other five are arthrobranchiae. The two remaining gUIs 

 are podobranchise, and belong to the second and the 

 third maxUUpedes 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 

 arthrobranchiae ; while the gill of the podobranchia of 

 the third maxiUipede is short and triangular, and fits in 

 between the bases of the second and the third arthro- 

 branchiae. The epipodite of the third maxiUipede 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 gUls, and 

 doubtless serves to keep them clear of foreign bodies. 



