CARCINUS 



409 



those of the second and third maxillipeds in the hypobranchial space 

 below the gills. Their function is the cleaning of the gills. 



In front, the gill chamber narrows to an exhalant passage^ which 

 contains the scaphognathite and leads to the large anterior opening. 

 The scaphognathite, working to and fro, drives water out of this 

 opening and so draws in a current through the other apertures. The 

 opening in front of the chela can be closed by a flange on the coxopo- 

 dite of the third maxilliped, and so the current can be regulated. The 



pb.mp^s 



pb.mp.2 



plb.i 



ar.ch. 



Fig. 287. A dorsal view of the organs in the left branchial chamber of Car- 

 cinus maenas. From Borradaile. ab. abdomen; ar.ch. arthrobranchs of the 

 cheliped; ar.mp.z, arthrobranch of the second maxilliped; ar.m^.3, arthro- 

 branchs of the third maxilliped; ep. i, base of the mastigobranch of the first 

 maxilliped; i.r. inner layer of the branchiostegal fold, reflected; pb.mp.2, 

 pb.mp.2, podobranchs of the first and second maxillipeds; pel. pericardial 

 lobe, a thin fold of the body wall, of undetermined function; plb.i, plb.2, 

 first and second pleurobranchs ; p.hy. posterior opening of the hypobranchial 

 chamber; scl. sclerite which keeps open the entrance to the exhalant passage; 

 scp. scaphognathite. 



water which enters this opening is prevented from taking a short cut 

 to the exhalant passage by a large expansion of the base of the mastigo- 

 branch of the first maxilliped, which directs it under the gills. The 

 current from the openings over the legs also passes under the gills. 

 All the water then passes upwards through the gills into the epi- 

 branchial space above them and so to the exhalant passage. Thus the 

 gills are thoroughly bathed. 



Owing to the width of the body the sterna are more easily dis- 

 tinguished than in the crayfish. Those of the maxillulary to second 



