88 PROFESSOR J. C. EWART AND MR J. C. MITCHELL ON THE 



in addition to distinguishing the simple (ampullary) from the branched (sensory) canals, 

 noted and described the expansions, now usually known as the ampullae of Lorenzini, 

 at the inner ends of the simple canals. Keference was also made to the work of Monro 

 secundus, who, in his memoir "On the Structure and Physiology of Fishes" (1785), 

 figures, without describing, several of the sensory as well as the more important am- 

 pullary canals. The most ambitious paper since the time of Monro, dealing with the 

 lateral sense organs of the skate, is one by Sappey (3). Unfortunately, Sappey's account 

 of the sensory canals is far from complete, and there is no reference to their innervation. 

 The groups of ampullae are described as glands for secreting mucus, and the ampullary 

 canals as ducts for conveying the mucus to the surface ; and all the ampullae are said to 

 be supplied by the trigeminal nerve. It is difficult to make out which of the skates 

 Sappey examined. From the drawings it appears to be R. clavata, but the arrangement 

 of the canals in both clavata and batis very decidedly differs from Sappey's figures. 



Three other investigators have considered at some length the lateral sense organs of 

 the skate, viz., Merkel, Garman, and Fritsch. Merkel (4) evidently foiled to make out 

 the arrangement of the sensory canals in the skate, more especially the hyomandibular 

 canal, which is represented in one of his figures as springing from the great lateral canal, 

 a condition which does not obtain in any Elasmobranch. 



Garman (5), following Agassiz, studied the sensory canals mainly with a view to 

 determining their value in classification. To admit of this, he examined and prepared 

 outline figures of the canals of a large number of skates and rays. Necessarily, the 

 descriptions are very short, and, as pointed out in the previous paper, there is no attempt 

 to consider. the canals either in reference to their development or innervation, with the 

 result that a somewhat complex nomenclature has been introduced. Nevertheless, the 

 figures and short descriptions of a large number of species cannot but be of service to the 

 comparative morphologist as well as to systematists. Again and again we have found 

 them most useful. Fritsch (6), in addition to giving a short account of the canal system 

 of the torpedo, has described a special form of sense-organ in the skate, to which he has 

 given the name of " spalt-papille." Fritsch's spalt-papillse probably correspond to the 

 minute pit organs of Amia, Mustelus, and Squatina. 



The four main sensory canals are related to the same nerves as in Laemargus. The 

 supra-orbital (S.O. 1 " 5 , figs. 6 and 7, PI. III.), or canal of the ophthalmicus superficialis branch 

 of the facial, runs forwards above the eyeball, pierces the snout, and then extends back- 

 wards external to the nasal capsule to communicate with the infra-orbital. The infra- 

 orbital (I.O. 1-8 , figs. 6 and 7), or canal of the buccal nerve, passes downwards and forwards 

 external to the eyeball, and then backwards along the ventral surface to bend inwards 

 and forwards after communicating with the supra-orbital and the hyomandibular. The 

 hyomandibular (HM 1-0 ., figs. 6 and 7), or canal of the hyomandibular nerve, is far more 

 extensive than in any of the sharks, though (as in sharks) the hyoid portion is absent 

 and the mandibular portion is incomplete and disconnected. Beginning where the 

 infra-orbital bends sharply inwards, it forms a long ventral loop, and then reaching the 



