The Lateral Line System in Siluroids. 539 



The opercular canal is innervated by the hyomaudibular nerve 

 which perforates the hyomandibular. After the hyoid nerve passes 

 downwards a branch proceeds forwards and supplies successively or- 

 gans 2 and 1 in the preoperculum and then organ 1' in the inter- 

 operculum. The great recurrent branch of the Facial leaves 

 the complex of ganglia belonging to Trigeminus and Facial dorsally 

 and proceeds upwards to the parietal bone in which it lies for part 

 of its course receiving the supratemporal branch of the first Vagus 

 branch and giving off more posteriorly the branch which passes by 

 the 1st spinal ganglion on its way probably to the pectoral fin. 



Branches x and y are given off" anteriorly from the dorsal region 

 of the same ganglion complex. They do not supply lateral line organs. 



Comparison of the several forms. 



Clarias and Auchenaspis (Figs. 1 and 2). Both of these 

 are African Siluroids and as might be expected the morphological 

 differences in their mucous canal systems are slight. Clarias is more 

 primitive in that the canals are of almost uniform calibre throughout 

 and there is less manifestation of the tendency of the terminal por- 

 tions of the canals to become functionless and rudimentary. In Cla- 

 rias also the sense organs and pores occur in the terminal portions 

 of the supra- and infraorbital canals at much more regular intervals. 



In both forms the infraorbital system possesses 5 sense organs 

 and 6 pores and these may be considered as corresponding each to 

 each, for not only do the numbers agree but the nerve twigs follow 

 the same courses. Branches 5 and 6 do not in Auchenaspis show 

 so markedly as in Clarias that extension and direction on which I 

 wish to lay special stress. As the dermal bones are much reduced 

 in Auchenasxns the close relationship of pores to sutures, which 

 exists in Clarias is not seen. 



In neither Clarias nor Auchenaspis is there any sense organ be- 

 tween pore 6 and the junction with the supraorbital. In the supra- 

 orbital system Clarias possesses 6 sense organs and Auchenaspis but 

 5. Pores 1 and 2 in Auchenaspis are situated at the ends of long 

 branches which cannot be considered primitive. The space between 

 sense organs 1 and 2 is great in Auchenaspis, the snout being con- 

 siderably elongated. In both forms branch 3 is directed outwards 

 and backwards behind the nose. Branch 4 which in Auchenaspis di- 



