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2. The Modification of the Swim-bladder in Hill-stream 
By SunpEer Lat Hora, M.S8c., 
Assistant Superintendent, Zoological Survey of India. 
(Read at the Ninth Annual Meeting of the Indian Science Congress and 
communicated with the permission of the Director, Zoological Sur- 
vey of India.) 
In the taxonomy of fishes great importance is attached 
to the presence, form and position of the swim-bladder. It 
is supposed to be a hydrostatic organ and its size and extent, 
so far as I know in Cyprinoidea, is directly correlated with 
the performance of this function. In a typical Cyprinoid 
fish, such as Labeo rohita, the bladder is large and lies free 
in the abdominal cavity. It is constricted in the middle to 
form an anterior and a posterior chamber and is joined to the 
oesophagus through a pneumatic duct which opens in its con- 
stricted region. In those Cyprinoid genera that live in rapid- 
running waters and consequently lead a ground-habit of life, 
the bladder undergoes considerable degeneration ; this consists 
firstly in the gradual reduction of the two chambers and the 
ultimate disappearance of the posterior, and secondly in the 
thickening of the walls. In extreme cases such as some 
processes of the adjacent vertebrae. 
In the genus Psilorhynchus, the members of which in- 
habit the torrents of north-east Bengal and Assam, the pos- 
terior chamber is greatly reduced and the anterior is covered 
by a thick fibrous coat. In Nemachilus vittatus, known from 
the lakes and streams in the Kashmir Valley, the anterior 
chamber is laterally flattened and covered by a bony capsule, 
while the posterior chamber is smal] and thick-walled. The 
pneumatic duct is still present. In Adiposia rhadinaea, the 
are connected by a canal, while the posterior chamber is 
minute and bulb-like; the whole of the bladder is enclosed 
in bone and the pneumatic duct has disappeared. In several 
specics of the genus Nemachilus the structure is very similar 
to that described in Adiposia rhadinaea with this differ- 
ence, that the posterior chamber vanishes altogether. In 
extreme cases such as Balitora brucei, the two lateral portions 
of the anterior chamber are much reduced and are somewhat 
separated from each other. 
