276 THE COMPARATIVE MORPHOLOGY 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 phyllobranchiae. 

 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 pleurobranchiae, the 

 other five are arthrobranchias. The two remaining gills 

 are podobranchia?, 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 

 arthrobranchiffi ; 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- 

 branchise. 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. 



