300 REPORT ON FISHES. PART i: COBITIDAE 



ECOLOGY AND STRUCTURAL MOPtFICATIONS 



Ecologically, the eight species nf tlie .i;cinis Xi'iiunliihts represented in tlu' cullectiMU nf 

 the Yale North India Expedition may I)e divided into three "associations": (i) llottmn- 

 dwelling species of the lakes, snch as A^ 7'ittati(s, which live in 4 tn 6 feet of water Init 

 lirohably rise from the Ixjttom occasionally and swim al)out ; ( ii ) lK)ttoni-(lwelling species in 

 torrential streams, such as A', stolicckae, N. gracilis, N. niicrops and X. tcnuicaiida. wliicli 

 haliitually live atlliering to rocks and stones in swift currents though at times, especially dur- 

 ing the i)reeding season, mav enter into sjirings, pools and lakes; (iii) free-swimming lake 

 species, such as N. deTerrai, N. hutchinsoni and N. panguri. wiiicli swim alxnit freely 

 in still waters luit for feeding purposes have to cling to rocks and otlicr ohjects, usually at 

 the lK>ttom. ("orreiated witli the al>ove differences in hahits and habitats, the species have 

 undergone remarkable modifications in the structure of certain organs. 



Air-bladder. In 1930, P referred to the modifications of the air-bladder in species of 

 Nemachilus from several localities and indicated the close relation I)etwcen its structure and 

 the type of habitat in which the species lived. On account of the occurrence of gradations 

 Ix'tween the Ncmacliiius-typc of bladder and the Dif^lophysa-iype of bladder, it was indicated 

 tliat the differences in the structure of the bladder could not be used for taxonomic pur|)Oses. 

 Rendahl'^ has, however, used this character in proposing several sub-genera for the species of 

 A^cjiiarliilus obtained by Dr. Sven Hedin in Central Asia, and has given a detailed morpho- 

 logical account of the modifications observed by him. The accompanying figure shows some 

 of his illustrations and an attempt is made below to explain the possible significance of these 

 modifications, as I interpret them. 



The structure of the air-bladder of A', barbutiila ( Text-Hgure 11'") is characteristic 

 of the species that live in swift currents and, though they may dart from place to place, are 

 rarely seen to swim. In these circumstances, the air-bladder has lost ils biioy.uit function 

 and its anterior portion is represented by two small lateral chambers {a) enclosed in bony 

 capsules and the posterior chamber by a small, thick-walled bag (c). This type of struc- 

 ture is found in A'^. stoliczkae, N. gracilis, N. niicrops and A'^. tcnuicauda. In N. yarkandcn- 

 sis (Text-figure ID) the fonn of the bladder remains the same but the lateral chamljers 

 are greatly enlarged so that they come in close contact with the skin. Tn the areas of contact, 

 the Ixiny capsules are incomplete so that the bladder can react to the surrounding changes 

 in pressure. The structure of the bladder in .Y. yarkandcnsis is more or less similar to that 

 of A^ vittatus (Hora 1930, Text-figure 6c) and probably the habits and habitats of the former 

 are similar to those of the latter. A'^. vittatus is a lake species and the Yale North India I'-xjic- 

 dition obtained several specimens, mostly from the weedy marginal areas of the Kashmir 

 lakes. Probably the species lives at or near the bottom and does not swim about niucli. 

 The Netherlands Karakorum Expedition obtained specimens of A'^. yarkandcnsis from pools 

 in the neighbourlioo<l of extensive marshes at Rabat-Utsang. The real lake forms that move 

 al)ont in all possible directions are characterised by a bladder of the type found in N. stnvarli 

 (Hora 1<'*30. Text-figure 8), ^V. hiitjertjuensis (Text-figure lA) and three new species of 

 Nemachilus described hero from Western Til>et (Text-figures 5/), //;, '^t). The posterior 



'Hora, Jount. Homlmy Nat. Hisl. Soc. XXXIV, pp. 379-385 (1930). 

 "Rendahl, Arkiv for Zoologi XXV, No. 11, pp. 1-51 (1933). 



