XI 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 Zepidosiren closely resembles that of 
Fic. 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; Jg, 
undivided portion of the 
lung; 22, left lung; oes, 
oesophagus ; p.al, p.a?, 
the left and right pul- 
monary arteries; ph, 
pharynx ; p.v, pulmonary 
vein ; 7./, right lung ; v6, 
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.) 
= 
3 
= 
33 
Protopterus, and, as in the latter Dipnoid, the 
glottis seems to be furnished with an epiglottis.* 
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; (0) differences 
in shape and relative size; (c) the development of caecal out- 
growths; (d) the subdivision of its cavity by the formation of 
internal septa; (¢) 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”; (gy) 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. 
