504 



PEOF. T. W. BRIDGE OHf THE 



imperfections in the account given by the two distinguished 

 Prencli zoologists wliose names have been mentioned, or to the 

 existence of genuine variations in which iV. horneensis deviates 

 from N. Pallasii, I am not in a position to decide. Nevertheless, 

 and apart from the question of specific variations in the structure 

 of a particular organ, there are other features in the air-bladder 

 of If. horneensis, and more especially its connection with the 

 auditory organ, which, perhaps, are not without importance to 

 those interested in the study of the obscure but fascinating 

 problem of subaqueous audition. Tor these reasons I venture 

 to give a brief account of the air-bladder of If. horneensis, and, 

 as the organ has not hitherto been figured in any species of the 

 family, to supplement the description by suitable figures. 



I desire to express my grateful thanks to the Council of the 

 Eoyal Society for a grant from the Research Fund in aid of this 

 and other kindred investigations. 



II. The Gekeeal Structure akd Relations op the 

 Air-bladder. 

 The specimen examined was 38 cm. long, and to this length 

 the postanal portion of the body or tail contributed 28 cm. 



Tor convenience in description, the air-bladder may be said to 

 consist of three well-defined portions, which, from their regional 

 disposition, may be termed (1) the anterior or pre-ccelomic, 

 (2) the abdominal or ccelomic, and (3) the caudal or post-coelomic. 



Lateral view of the air-bladder of Notopterus borneensis. About two-thirds 

 nat. size, ab.p, abdominal portion ; l.c.c, left caudal cjeeum ; d.p, ductus 

 pneumaticus ; f.c, filiform caeca ; l.a.c, left auditory caecum ; oes, oesophagus ; 

 sb.s, subspherical sac ; t.p, its tubular prolongation ; v.d, ventral diver- 

 ticulum. 



The abdominal portion (see fig., ah.p.) is more or less cylin- 

 drical in shape, but much deeper behind than in front, and 



