The Lateral Line System in Siluroids. 531 



normally between the fourth and fifth and fifth and sixth pores re- 

 spectively. 



Supraorbital canal. This canal commences with a pore 

 placed far laterally on the snout near the base of the first barbule. 

 From this pore a long branch passes towards the median line in front 

 of the terminal pore of the suborbital system. Arriving nearly at the 

 middle line it runs backwards alongside the specially solid dermeth- 

 moid but not enclosed in bone. It does not communicate it with its 

 fellow of the opposite side. After passing a short distance backward 

 the canal gives off a branch outward which opens at a pore, the se- 

 cond, close to the first of the infraorbital line. At the origin of this 

 branch lies the small first sense organ. 



From this point the canal runs straight backwards. The second 

 sense organ lies at the level of the nasal opening and the third pore 

 just beyond the same. Hitherto only feeble bone has been developed 

 in the inmiediate neighbourhood of the sense organs but shortly the 

 canal passes into the substance of the frontal bone. The third sense 

 organ occurs at the level of the front of the orbit and close to it a 

 rather large branch is given off which passes towards the middle line 

 and splitting dichotomously opens by two pores, 4a and 4b. The 

 canal then takes an outward and backward direction and at the level 

 of the middle of the eye contains the fourth sense organ. Posteriorly 

 to this the large branch containing the 5th sense organ is given off 

 towards the crown of the head. The canal passes outwards, joins 

 the infraorbital and is then continued backwards as the main canal 

 of the body. 



Main canal. This continues straight backwards from the junction 

 of the supra- and infraorbital systems and at the level of the broadest 

 part of the skull is found the sixth sense organ. Close to this the 

 operculo-mandibular canal passes off laterally. In the squamosal bone 

 lie the seventh, eighth and ninth sense organs. Between the seventh 

 and eighth a branch passes off outward and backward and opens in 

 a pore, No. 7, just beyond the edge of the dermal bones of the skull. 

 The branch given off" between the eighth and ninth sense organs passes 

 inwards and backwards and opens in the dermis between the pro- 

 jecting angles of the squamosal and parietal bones. The ninth sense 

 organ is the last belonging to the head. 



Operculo-mandibular canal. The first pore is situated 

 on the under surface of the lower jaw near its extremity. From it 

 a tube curves forwards and upwards passing into the dentary bone 



