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Show 2395.1 SBNSOBY CANAL SYSTEM Oi ElSHES. 275 are described in detail. In all, the system is described in four families viz. the Siluriclce, Esocidee, Salmoniclce, and Murcenidee, which include eight different species referable to seven genera. To Professor T. W . Bridge, M.A., of Mason College, Birmingham, I wish to offer m y sincere thanks for the specimens of Clarias, Callichthys, and Pimelodus, and for the very generous and continued assistance which he has given m e ; also to Professor W . C. M'Intosh, M.D., F.E.S., for his kindness in granting m e the use of a table at the St. Andrews Marine Zoological Laboratory, during the Long Vacation of 1893. M y thanks are also due to Dr. G-iinther, F.R.S., who has identified for m e the specimens of Pimelodus and Labeo. II. SlLUBIDJS. The sensory canal system of certain genera of this family has been previously described by Ramsay Wright (12) and Pollard (11). The former has given a brief account of the canal system in Amiurus catus and a more detailed account of the cranial nerves. Pollard has described and figured the system and its innervation in Clarias, Callichthys paleatus, Auchenaspis biscutatus, Trichomyc-terus tenuis, and Chcetostomus guairensis. Except in Clarias, he interpreted both the distribution of the sensory canal system and cranial nerves from a series of young specimens cut into sections. Although the cranial nerves of the Siluridce are somewhat difficult to follow, I have preferred dissection as a means of investigation, and it will be noticed on comparing the figures of this author with those here given that there are many points of difference. The canal system has been worked out in Clarias nieuhofii, Amiurus catus, Pimelodus maculatus, and Callichthys littoralis. The cranial nerves in Clarias magur, Amiurus catus, and Pimelodus maculatus. 1. CLAEIAS NIEUHOFII 2 General Description. The sensory canal system commences as an exceedingly fine canal slightly in front of the base of the caudal fin. A s it passes forwards its diameter increases. There are a series of pores opening into the canal, distributed at somewhat regular intervals. The canal traverses the region of the post-temporal and into the squamosal, from which point it m a y be regarded as the main canal of the head. It gives off a short backwardly directed branch, and immediately in front of this the operculo-mandibular branch arises (PI. XVIII. fig. 1, Op.Mnf). Prom the squamosal the main canal continues along the dorsal border of the sphenotic, and divides into supra- and sub-orbital branches (PI. XVIII. fig. 1) : the former passing through the frontal and lateral ethmoid (Parker) and giving off in its course three smaller branches and a commissure in 1 The specimen upon which all measurements, &c, were made was 360 millim. long. 18* |