630 ALLIS. [Vou. XII. 
of Amiurus, as in Amia, it is a direct continuation of the line 
of the supraorbital canal organs. Those on the side of the 
head in Silurus are one vertical, one horizontal, and one on the 
hind end of the mandible; the lines do not, however, have the 
same positions relatively to each other that they have in Amia. 
The arrangement of the canals in larvae of Amiurus shows 
beyond question that Pollard’s pore 6 infraorbital in Clarias is 
formed by the fusion of pores 6 infraorbital and 6 supraorbital, 
his pore 6 supraorbital being therefore in reality pore 7 of that 
line, and the terminal pore of the line. That it is the terminal 
pore of the line is shown sufficiently by the presence of a 
sense organ in what Pollard considers as its tube, and by the 
absence of such an organ in what he considers as the continua- 
tion of the main canal. Pore 7 of the main canal in Clarias 
has fused with the terminal pore of the operculo-mandibular 
canal and is found on that line, but not shown in Pollard’s 
figure, and pore 7 in his figure is in reality pore 8. The same 
is true of Auchenapsis and Chaetostomus. In each of these 
fishes the last pore and tube of the ascending portion of the 
suborbital canal, behind the eye, is a double system, formed by 
the fusion of a suborbital and supraorbital pore and tube; and 
the last pore and tube of the operculo-mandibular canal is also 
a double system, formed by the fusion of a tube and pore of 
the main line with the terminal pore and tube of the operculo- 
mandibular line. 
The sense organs of all the canals in all the fishes described 
by Pollard are, therefore, with a single exception, regularly 
placed one between each two consecutive tubes of the line to 
which it belongs, instead of being irregularly placed, as the 
figures and numbering used by Pollard would indicate. The 
single exception, or apparent exception, is in the operculo- 
mandibular line in Chaetostomus, where one organ seems to 
be wanting, but the development, if it were known, would 
undoubtedly show that the irregularity even here is only 
apparent. In Chaetostomus the operculo-mandibular canal 
turns backward and downward into the interoperculum and con- 
tains an organ in that bone. This may be another instance of 
a pit line in one form becoming a canal in another, for in Gadus 
