XI AIR-BLADDER 303 
cavity into the tail, sometimes penetrating for a short distance 
into the expanded haemal canal of the anterior caudal vertebrae, 
or extending unsymmetrically along either the right or left side 
of the tail. More frequently, perhaps, where the air-bladder is 
prolonged into the tail, it assumes the form of two bilaterally 
arranged and symmetrical caeca, which extend backwards for 
a variable distance internal to the caudal muscles and in contact 
with the adjacent skeletal elements, as in Notopteridae, and in 
some Sparidae, Carangidae, and Scombridae. The extension of 
the air-bladder into the tail is often associated with a short, 
laterally-compressed trunk, which, if the bladder is to attain its 
normal degree of development, necessitates its prolongation into 
the caudal region. 
(c) A characteristic feature in the air-bladder of many 
Teleosts belonging to widely different families is the develop- 
ment of a more or less complex system of simple, or vari- 
ously branched, caecal outgrowths, which, like the internal septa, 
are specially characteristic of those Fishes in which the bladder 
is used as a vocal organ without, however, being peculiar to 
them. 
in some of the Gadidae, as in the Cod (Gadus morrhua), the 
air-bladder divides anteriorly into a pair of caecal prolongations 
which extend forwards to the head, and are often curiously 
coiled. Somewhat similar caeca are also present in species of 
Berycidae, Sparidae, Siluridae, Clupeidae, and Notopteridae. 
Caecal prolongations may also be developed from the hinder end 
of the bladder, and, as already mentioned, extend into the tail; 
or even from both ends in the same species (e.g. Notopterus).’ 
In the Silurid, Rita crucigeraZ a long tubular caecum is 
developed from each side of the heart-shaped bladder, and 
thence is prolonged backwards to the anus. In certain species 
of Doras of the same family (e.g. D. maculatus), an elegant 
series of variously sized branched caeca fringe each of the lateral 
margins of the bladder. It is, however, in the Physoclist family 
of the Sciaenidae * that the branching of the air-bladder attains 
its greatest development in extent and variety. 
1 Cuvier and Valenciennes, Hist. Nat. d. Poissons, xxi. 1848, p. 139; Bridge, 
Journ. Linn. Soc. Zool. xxvii. 1900, p. 503. 2 Ways 2.2.8. 1871, ps Ale: 
3 Sérensen, ‘‘Lydorganer hos Fiske,” Copenhagen, 1884, p. 85; Kner, SB. k. 
Akad. Wiss. Wien, xi. 1853, p. 1388. 
4 Cuvier and Valenciennes, op. cit. v. 
