AIR-BLADDER 



305 



verse, or longitudinal constrictions already described, or by the 

 growth of simple or branched prolongations, the organ is often 

 chambered or sacculated by the development of internal septa 

 or partitions. 



In many of the Gurnards {Trigla) ^ the cavity of the bladder 

 is divided into two intercommunicating compartments by a 

 transversely - disposed 

 and centrally-perforated 

 diaphragm. The large 

 air-bladder of some 

 species of Erythrinus ^ 

 is subdivided internally 

 into numerous alveoli or 

 sacculi. In Notopterus 

 a longitudinal septum 

 divides the cavity of 

 the abdominal portion 

 of the bladder into two 

 lateral chambers, which, 

 however, freely inter- 

 communicate anteriorly. 

 In the great majority of 

 the Siluridae ^ the cavity 

 of the organ is divided 

 by a characteristic 

 T-shaped arrangement 

 of a primary transverse 

 and a longitudinal 

 septum into three com- 

 municating chambers, of which one is anterior and transversely 

 disposed, and two are posterior and longitudinally arranged (Pig. 

 222). The posterior compartments in many genera are still further 

 divided by the growth of secondary transverse septa, extending 

 outwards from the median longitudinal septum, without, how- 

 ever, reaching the external lateral walls of the chambers. In a 

 few genera, as in certain species of Pangasius^ additional fibrous 

 bands and ridges passing between the primary and secondary 



FlQ. 182. — Air-bladder of Pogonias chromis. 

 (From Cuvier and Valenciennes.) 



^ Moreau, Compt. Bend. lix. 1864, p. 436. 

 ^ J. Miiller, £er. d. k. Akad. d. Wiss. Berlin, 1842, p. 177. 

 ' Bridge and Haddon, op. cit. p. 234, PI. II. Fig. 18. 

 VOL. VII 



•• Ibid. p. 216. 

 X 



