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. NotoiJterus)} 

 In the Silurid, Rita crucigeraf 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. 



' Cuvier and Valenciennes, Hist. Nat. d. Poissons, xxi. 1848, p. 139 ; Bridge, 

 Journ. Linn. Soc. Zool. xxvii. 1900, p. 503. ^ Day, P.Z.S. 1871, p. 703. 



' Sbrensen, "Lydorganer hos Fiske," Copenliagen, 1884, p. 85 ( Kner, SB. k. 

 Akad. Wiss. Wien, xi. 1853, p. 138, 



* Cuvier and Valenciennes, op. cit. v. 



