Fishes of the Western North Atlantic 



483 



Figure hi. Manta birostris, juvenile male, 11 feet 5 inches wide, from Bimini, Bahamas. ^Anterior view 

 of part of branchial sieve, with gill folds (outer end toward right), from anterior side of first branchial arch, to 

 show general appearance, about 1.8 X. B Portion of same, showing (I) locations of gill plates and (II) line of 

 junction between transverse bars born \>y adjacent giU plates, about 6.5 X. 



zone occupied by the gill filaments, any contraction of the pharynx (as in breathing) 

 tends to bring the pinnate distal edges of the plates on each arch into contact with the 

 plates on the two adjoining arches along the outer sides of the latter, the plates along 

 the inner parts of successive arches continuing far apart (Figs, iio, 112 A). Con- 

 sequently, the only route by which the water that is expelled from the pharynx can 

 reach the external gill openings is via the meshes of the grid or sieve to the channels 

 that lead outward between the basal parts of adjacent gill plates. In this way, any small 

 animals that are taken in with the water through the mouth are retained within the 



3'* 



