Chap. 33 



VERTEBRATES — LOWER CHORDATES AND FISHES 



675 



Heart 



A operculum removed 

 exposing gills 



B Circulation through heart and gills 



Operculum Gills 



Esophagus 



D,E Horizontal section 

 from right to left 



Upper 

 jaw 



C Detail of circulation in gill 



Mouth 

 cavity 



D' 



Capillaries 



Blood 



from heart 



to gill 



Blood 



from gill 



to body 



Gill arch 

 Raker 



E' 



D,E Vertical section 

 dorsal to ventral 



D,D Intake of water E,E Outgo of water 



Fig. 33.12. Respiratory organs and breathing action of a bony fish. The circu- 

 lation of blood is shown in one gill; the structures in diagram (B) are shown 

 in the same position that they would be in the fish (A). The diagrams (D, D^ 

 and E, £i) represent the intake and outgo of water in one complete "'breath." 



