68 Records of the Indian Museum. [Vol. XXIV, 



quite different from the normal Cyprinoid bladder. The following 

 are the chief points of difference : — 



(i) There is a short pneumatic duct from the anterior end of 

 the bladder to the oesophagus, while in the normal Cyprinoid type 

 the pneumatic duct is long and opens into the middle of the 

 bladder in the constricted region. 



(ii) The bladder may or may not be constricted in the middle. 



(iii) The pneumatic duct is present only in young specimens, 

 while it is lost in the adult. 



In the genus Botia, the structure of the air-bladder differs 

 considerably. Though in many respects of a typical Cyprinoid 

 form, the anterior chamber is partially (fig. id) or wholly (fig. 

 le) enclosed in a bony capsule formed by the transverse pro- 

 cesses of the neighbouring vertebrae. On comparing drawings d 

 and j in figure i, it will be seen that Day was in error in suggest- 

 ing that the bladder of Diplophysa would have to be similar in 

 structure to that in Botia. 



The reduction of the swim-bladder in fishes that live in rapid- 

 running waters is in all probability due to the fact that they live 

 on the bottom and do not require to make vertical movements. 

 The enclosure of the bladder in a bony capsule presumably has 

 some special biological significance, but of this nothing is yet 

 known. Zugmayer believed that the free bladder in Diplophysa 

 is to be explained by the assumption that the members of the 

 genus have not yet acquired a true ground habit and that conse- 

 quently the posterior half has not yet been affected. This, how- 

 ever, does not appear to be a~ correct interpretation of the fact as 

 there are two distinct air-bladders in Diplophysa, the one enclosed 

 in a bony capsule being possibly the original Cyprinoid bladder, 

 while the other that lies free in the abdominal cavity is either a 

 secondary acquisition or, as Dr. Annandale suggests to me, repre- 

 sents the modified posterior chamber of the normal Cyprinoid 

 bladder. In the latter case the anterior chamber has become en- 

 closed in bone, as in Nemachilus vittatus, and the posterior cham- 

 ber was nipped off, retaining its connection with the oesophagus 

 through the primary pneumatic duct. The members of the genus 

 Diplophysa have in all probability come to live secondarily in the 

 deep muddy waters of the lake-basins of Central Asia in which 

 situation they require a hydrostatic organ for vertical movements ; 

 I believe that they have originated from forms like Nemachilus in 

 which the air-bladder is reduced and enclosed in a bony capsule. 

 When the primary air-bladder became enclosed in bone it probably 

 could not again be modified for the performance of a hydrostatic 

 function to suit the new environment. T thus believe that Diplo- 

 physa is a more specialized genus than Nemachilus, whereas Zugma- 

 yer regards it as more primitive. Of the species of Diplophysa at 

 present known, all described by Kessler, the following have been 

 recorded either from lakes or from deep muddy waters at great 

 altitudes in Central Asia : — 



