SEA-FISHERIES LABORATORY. 133 



pared with a good figure of the sensory canals of the 

 Skate, Ewart and Mitchell's for example*, it will he seen 

 that there is no doubt as to this interpretation. All the 

 canals figured in fig. 7, PL III. of the memoir cited are 

 present, though some are not clearly shown in the 

 photograph. That part of the infra-orbital canal lettered 

 1.0.4 to 1.0.5 by Ewart and Mitchell; the part of the 

 hyomandibular lettered H.M.; the sub-orbital S.0.4 to 

 S.0.5; and the infra-orbital 1.0.6 to 1.0.7 are greatly 

 dilated, and some of these dilatations present themselves 

 as vesicles about 3'5 cms. in diameter, and raised up above 

 the general level of the skin by as much as 1*5 cm. 

 Some of the canals are not much greater in calibre than 

 in the normal fish: these are the infra-orbital 1.0.7 to 

 1.0.8; the supra-orbital S. 0.3 to S.0.4; the infra-orbital, 

 1.0.3 to 1.0.4, and 1.0.6; and the hyomandibular 

 adjacent to its union with the infra-orbital. On a first 

 examination it appeared that some of the canals were 

 absent, but they were found beneath the floors of the 

 larger vesicles. This was the case with the hyomandi- 

 bular, and part of the supra-orbital. In these cases the 

 hidden canals were of the normal calibre. 



There is not nearly the same amount of dilatation 

 of the canals on the dorsal surface of the head ; but the 

 two supra-orbitals 1.0.7 to 1.0.8 are dilated, the greatest 

 diameter being about 1'5 cm. In front and external to 

 the left orbit there is also a large and complex cyst, 

 which is about 4 cms. in diameter, is raised up above 

 the general surface of the skin about 1 cm., and is 

 depressed below the surface about 1'5 cm. It occupies 

 the place of junction of the hyomandibular and infra- 

 orbital canals, and is almost certainly made up of 



* Trans. Roy. Soc. Edinburgh, Vol. 37, 1891-2, pp. 87-105, pi. Ill, 

 fig. 7. 



