VISCEEAL ANATOMY OF THE CHAEACINID.^. 



67 



further forward, the condition is precisely that which is commonest amongst the 

 Cliaracinidae. 



Thus far, the facts are in accordance with Sagemehl's hypothesis. 

 In turning, then, my attention to the Siluridse, I Avas prepared to find conditions 

 similar to those above described. To ray surprise, however, investigation revealed a 

 precisely opposite state of things, for in these fishes the opening of the ductus pneu- 

 maticus is actually and unquestionably on the right side of the mid-dorsal line of the 

 oesophagus (PI. 4. figs. 16 and 17)— as far, indeed, to the right as it is in most Characinids 

 to the left. 



There may possibly he some significance in the fact that, in all the Siluroids examined, 

 the pyloric flexure of the stomach was found to be lateral and to the left side. But, 

 after careful observation and consideration, I am unable to see that this modifies the 

 relations of the ductus pneumaticus with the oesophagus as above stated. 



This statement is based upon the examination of forms taken from the following 

 eight widely divergent genera, more than one specimen iu most cases having been under 

 examination : — 



Amiurus [A. nebulosus) , 



Clarias (C. lazera) (fig. 16), 



Sijnodontls (S. f/ambiensis), 



Malapterurus [M. electricus) (fig. 17), 



Chrysichthys (C. auratus), 



Siluranodon [S. auritus), 



Schiihe [S. mi/sttis), . # 



Auchenoglanis {A. biscutatm). 



In seven out of the eight the opening of the duct was decidedly on the right side. In 

 the eighth case — Siluj-aiiodoii — it appeared to be median ; but in this case, and in this 

 case alone, it has to be stated that the condition of the viscera was unsatisfactory and 

 precluded a positive verdict. 



Bridge and Haddon *, in their detailed study of the air-bladder in the Siluroid fishes, 

 describe the median connection of the ductus pneumaticus with the bladder itself but 

 make no reference to its precise relation with the oesophagus. 



Of the Gymnotidse, the fourth family of those fishes Avhicli possess the Weberian 

 apparatus, I have examined three species from two genera — 



Carajtiis fdsciatus (1 specimen), 

 Steriiopyyus curupus (2 specimens) (fig. 18), 

 Sternopygus virescens (3 specimens); 



with the result that the pneumatic duct was found to open into the oesophagus in the 

 median dorsal line in Carapns and on the left side in both species of Sternojji/fftis (tig. 18). 

 The duct may thus fairly be described as having a tendency towards the left side. 



r 



* " Contributions to the Anatomy of Fishes : the Air-Bladder and Weberian Ossicles in the Siluroid Fishes," 

 Phil. Trans., B. vol. 184, 1S93. 



