AIR-BLADDER 



301 



Vertebrata. Non-striated muscle cells, pigment cells, and blood 

 capillaries are abundantly present in the connective tissue 

 external to the lining epithelium of the lung-cavities. . 



The air-bladder of Lepidosiren closely resembles that of 



FIG. 178. A, the air-bladder 

 of Protopterus, viewed 

 from the ventral side. 

 Portions of the ventral 

 walls of the pharynx and 

 bladder have been re- 

 moved, gl, Glottis ; Ig, 

 undivided portion of the 

 lung ; l.l, left lung ; oes, 

 oesophagus ; p.a 1 , p.a' 2 , 

 the left and right pul- 

 monary arteries ; ph, 

 pharynx ; p.v, pulmonary 

 vein ; r.l, right lung ; vb, 

 vestibule. (From Newton 

 Parker.) B, portion of 

 one lung of Protopterus, 

 opened from the dorsal 

 side to show the alveoli. 

 al, Alveolus. (From Bald- 

 win Spencer.) 



r.i- 



Protopterus, and, as in the latter Dipnoid, the 

 glottis seems to be furnished with an epiglottis. 1 

 In all the Dipnoi the air-bladder is highly 

 vascular, but nevertheless presents no trace of 

 " red bodies " or " red glands." 



The most striking features in the remark- 

 ably polymorphic air-bladder of Teleosts relate 

 to (a) its presence or absence ; (&) differences 

 in shape and relative size ; (c) the development of caecal out- 

 growths ; (cT) the subdivision of its cavity by the formation of 

 internal septa ; (e) the retention or suppression of the ductus 

 pneumaticus, and the occasional development of secondary ducts 

 communicating directly with the exterior ; (/) the presence of 

 " red glands " or " red bodies " ; (g) its connexion with the audi- 

 tory organ ; (&) its adaptation as an organ for sound-production. 



1 Bischoff, Ann. d. Sci. Nat. (2) Zool. xiv. 1840, p. 136. 



