The Lateral Line System in Siluroids. 541 



innervation is essentially the same in both. A ramus mandibularis 

 of the Facialis is present though there is, no trace in the latter of 

 a corresponding mucous canal. In Triclioniyderus also tlie nerve 

 from the great Recurrens facialis which proceeds to the pectoral fin 

 arises far forward at the level of the 5th sense organ and then runs 

 comparatively near the surface directly crossing the space in which 

 lie the slight expansion of the canal between pores 6 and 7 and the 

 bladder leading to the sacculus. 



Comparing Chaetostomus, another South American forni, with the 

 two last a remarkable ditîerence is seen which may however be in 

 great part due to difference in age of the specimens. Thus in Chaeto- 

 siomus the sense organs and pores, and even canals are more numerous. 

 In place of the two sense organs of Trichomyderus or three in Call- 

 ichthys there are in Chaefostomus 6 present in the infraorbital system. 

 In the last named the infraorbital canal is much extended distal ly 

 corresponding to the extension of the snout in front of the nose. In 

 Triclioniyderus the elongation of the snout has taken place more 

 behind the nose. Thus probably from its relations the 3rd sense organ 

 in Chaetostomus corresponds to the 1st in Trichomyderus. Sense organ 

 2 in the latter and 3 in CallichtJujs are not present at all in Chaeto- 

 stomus ^ ). 



In the supraorbital canal the resemblance is greater but sense 

 organ 2 of Chaetostomus is wanting in the others and in them also 

 there is no trace of the median branch containing sense organ 5. The 

 pore at the junction of supra- and infraorbital systems is closed in 

 Chaetostomus. The canal in the iuteroperculum of the last is not 

 present in the other two and of them only Callichthys possesses 

 a preopercular canal. Its two sense organs correspond with those of 

 Chaetostomus but the canal does not join the main canal. 



Simple pores in Trichomyderus and Callichthys often represent 

 branches or commissures in Chaetostomus. Thus the transverse com- 

 missure in the frontal is only represented by pores 3 and 4, respectively 

 in the former pore 7 by the half pore or pore 3, branch 8 by pore 6. 

 No great differences in the innervation are to be noticed except for 

 the peculiar position in Trichomycterus of the sensory nerve which 

 proceeds to the pectoral fin. 



Chaetostomus and the African forms. On comparing the 

 mucous canals of Chaetostomus, Clarias and Auchenaspis the truly 



1) Unless a shifting downwards has occurred in Ch. 



Zool. Jahrb. V. Abth. f. Morph. 36 



