par 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 (7'rigia)' 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 
saccul. 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 (Fig. 
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 
Fic. 182.—Air-bladder of Pogonias chromis. 
(From Cuvier and Valenciennes. ) 
Moreau, Compt. Rend. lix. 1864, p. 436. 
J. Miiller, Ber. d. k. Akad. d. Wiss. Berlin, 1842, p. 177. 
Bridge and Haddon, op. cif. p. 234, Pl. II. Fig. 18. + Tid. p. 216. 
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