DEVELOPMENT OF LUNGS AND BUOYANCY STRUCTURES 



643 



STURGEON 

 AND MANY 

 TELEOSTS 



ERYTHRINUS 



CERATOOUS 



RETE MIRABILE 

 ■INTESTINAL ARTERY 

 PORTAL VEIN 

 HEPATIC VEIN 



Fig. 304. Swim-bladder and lung relationships. (A-F slightly modified from Dean: 

 Fishes, Living and Fossil, 1895, New York and London, Macmillan and Co.; G after 

 Goodrich, '30.) (A-E) Sagittal and transverse sections of swim-bladder relationships. 

 (F) Lung relationship of Dipnoi and Tctrapoda. (G) Diagram of physoclistous swim 

 bladder of teleost fish. 



most teleost and ganoid fishes. In elasmobranch and cyclostomatous fishes, the 

 air bladder is absent. Two main types of air bladders are found: 



(1 ) a physoclistous type (fig. 304G), in which a direct connection with the 

 pharyngeal area is lost (e.g., the toadfish, Opsanus tan), and 



(2) a more primitive physostomous variety (fig. 304A-E), retaining a 

 pharyngeal or pneumatic duct (e.g., the common pike or pickerel, 

 Esox Indus ) . 



One function of the air bladder presumably is to alter the density of the 

 fish in such a way as to keep its density as a whole equal to the surrounding 

 water at various levels (Goodrich, '30, p. 586). Buoyancy, therefore, is one 

 of the main functions of the air bladder. 



The air bladders of fishes, in some cases at least, have both respiratory or 

 lung and buoyancy functions (Goodrich, '30, pp. 578-593). In the bony 

 ganoid fishes, Amia calva and Lepisosteus osseiis (fig. 304B), the air bladder 

 apparently has a primary function of external respiration and, therefore, may 



