262 PROCEEDINGS OF THE CANADIAN INSTITUTE. 
(b) Nerve-Hillocks. 
(1). SENSE ORGANS OF THE LATERAL LINE AND or THE ‘Mucous’ 
CANALS OF THE HEAD. 
The system of cutaneous canals which lodge from place to place 
the sensory nerve-hillocks was at one time described as the system of~ 
‘mucous’ canals, owing to the belief that the skin owes its slimy 
surface to the secretions of these. It is now very well known that 
the sliminess is due to the mucus-cells described above, and that 
any mucus which is found in the interior of the canal system has the 
same sort of relation to the nerve-hillocks as the endolymph in the ~ 
auditory labyrinth to the maculew acusticw. The fact that the canal 
system has a very free communication with the outside, renders it 
probable that the surrounding medium must penetrate it in such a 
way as to dilute any mucus present. 
The canal system in Am/wrus possesses the arrangement which is 
commonest among Teleosts, that is to say the canal of the lateral 
line is entirely imbedded in the cutis, and opens only from place to 
place by the pores, while it communicates anteriorly with the more 
complicated canal system’ of the head. In other Teleosts the scales 
of the lateral line are modified in various ways both by the presence 
of the canal and its pores, but as these are entirely absent in 
Amiurus, the pores are simpler in their structure. It is very much 
easier to study the apertures of the canal in the fresh condition than 
in a preserved specimen, owing to the absence of pigment in the 
immediate neighbourhood of the pores, and to the fact that their 
edges are somewhat swollen. 
All of the lateral pores are similar in character, with the exception 
of the two terminal pores, which are near the caudal fin, and which 
open obliquely into a small detached portion of the canal. This is, 
no doubt, a relic of the interrupted lateral canal seen in other 
Physostomous forms e.g. Hsow. Forty pores are present on each 
side ; as the number of pores corresponds to the number of nerve- 
hillocks (although opening into the canal at some little distance from 
these), and the spinal nerves are also present in the same number, 
it is obvious that the sense organs of the lateral line are disposed 
in a metameric fashion here as in other Teleosts. 
The lateral canal corresponds exactly in position to the cleft 
between the dorsal and ventral divisions of the lateral musculature. 
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