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Show 1895.] SENSOBY CANAL SYSTEM OF FISHES. 279 line, and then uniting with the main infra-orbital. These later connections in Amia are not always found in other fishes ... in Amiurus catus although they unite to form a continuous line, they do not unite with the main canal1." I shall endeavour to prove that in Amiurus catus the operculo-mandibular branch does join with the main canal of the head. In the account given by Ramsay Wright (12. pp. 262-265) it is stated that the posterior portion of the lateral canal is detached from the remaining portion, which is scarcely correct, and that there is " no communication between the principal canal and that which is lodged in the preoperculum." Whether or not Professor Ramsay Wright regards the mandibular portion as distinct from the preopercular portion I am unable to gather from his account. O n p. 265 he speaks of " the canal which is lodged in the preoperculum and mandible " as if it were continuous; but on the same page he refers to the " independence of the mandibular branch,"-I take this to mean the operculo-mandibular branch. In Amiurus catus there is no true lateral canal. In the posterior portion of the body are a series of short isolated dermal tubes. The interruptions are more frequent and the tubes shorter in the posterior region than in the anterior. Posterior to the operculum there is a coalescence of these short tubes, and a distinct, but very fine, canal is formed. At the point where the lateral canal enters upon the head a short backwardly directed branch is given off (PI. XVIII. fig. 2, x), which passes over the supra-clavicle (McMur-rich). Immediately after entering the skull an occipital commissure (PI. XVIII. fig. 2, Oc.com.) is given off, which communicates with the main canal of the opposite side; a little further on a lateral branch passes off-the operculo-mandibular branch. The main canal passes forwards, giving off a short branch towards the median line, and posterior to the orbit divides into supra- and sub-orbital branches. The sub-orbital branch passes through a series of canal-bones forming a circumorbital series, from these it is continued forwards into the antorbital bone. The supra-orbital branch runs above the orbit, giving off at its junction with the main canal a short backwardly directed branch, which runs towards the mid-dorsal line; slightly in front of the orbit another similar branch is given off. Passing to the anterior region the supra-orbital branch traverses a small canal-bone (PI. XVIII. fig. 2) and terminates at the base of the maxillary barblet. Course of the Canals and Branches. 1. T H E L A T E E A L C A N A L consists of a series of isolated dermal tubes; in the posterior portion of the body they are exceedingly small, but become slightly larger in the anterior region. Each tube opens to the surface by one or more pores. Slightly behind the operculum the tubes anastomose with one another and form a fine canal, which gives off a backwardly directed branch 1 The italics are mine.-W. E. 0. |
