490 AUGUSTA LAMONT ON 



ampullae, the superficial ophthalmic contains considerably fewer, while only four to 

 six ampullae are innervated by a single small branch of the buccal nerve. In Raia 

 the total number may be taken to be in excess of this — in some species very greatly 

 so. According to figures and descriptions of the ampullary canals in Torpedo, the 

 canals appear to be less widely distributed over the surface than is the case even in 

 those rays which have the shortest and fewest canals. 



The ampullae of Trygon pastinaca are described by Leydig as representing the 

 next step in development above those found in Torpedo. Each ampulla has four big 

 sacculations which bulge out especially in a downward direction, as shown in Plate II, 

 fig. 4 of Roc/ten uud Haie, and which are not indented like those of Raia. The 

 ampullae are smaller than those of Raia clavata or Leviraia oxyrhynchus* and are 

 peculiar in having a yellowish colour. There are five pairs of ampullary capsules. 



The ampullary canal system of Raia thus appears in some respects to be more 

 highly developed than that of either Torpedo or Trygon. The number of its 

 ampullae and ampullary groups is in excess of those possessed by Torpedo, where 

 the hyoid and one of the buccal groups are absent ; and the individual ampullae are 

 more complicated in structure than those of either Torpedo or Trygon. On the 

 other hand, the much greater development of the mandibular group in Torpedo — 

 both relative to the same group in Raia, and to the other groups in Torpedo itself — 

 invites remark, reversing as it does the condition found in Raia, where that group is 

 always the least both in size and in number of the contained ampullae. 



BIBLIOGRAPHY. 



1664. Stenson, De Musculis et Glandulis Observationum specimen, etc., Amst., 1664. 



1669. Stenson, Elementorum Myologix specimen, etc., Amst., 1669. 



1678. Lorenzini, Osservuzioni intorno alle Torpedini, Firenze, 1678; London, 1705, Angl. 



1785. Monko, Alexander, The Structure and Physiology of Fishes, 1785. 



1801. St. Hilaire, Geopproy, "M^moire sur l'anatomie comparer; des organes electriques de la Raie 



torpille, du Gymnote engourdissant, et du Silure trembleur," Ann. Mus. Nat. d'Hist. Nat., 



1802, i, p. 392. 

 1813. Jacobson, " Extrait d'un memoire sur un organe particulier des sens dans les Raies et les 



Squales," Nouv. Bull. Sci. Societe Philom. Paris, 1813, vi, p. 332. 

 1820. Treviranus, G. R., " Uber die Nerven des Funften Paars als Sinnesnerven," Vermischte Schriften 



anatomischen und physiologischen Inhalts, Bremen, 1820, iii, pp. 135-146. 

 1822. Blainville, Traite des animaux : de leur organisation, ou principes d'anatomie comparee, Paris, 



1822, i. 

 1825. Knox, Robert, "On the Theory of the Existence of a Sixth Sense in Fishes, supposed to reside 



in certain peculiar Tubular Organs found immediately under the integuments of the Head 



in Sharks and Rays," Edinburgh (Brewster's) Jour. Sci., 1825, ii, pp. 12-16. 

 1828. Cuvier et Valenciennes, Histoire naturelle des poissons, Paris, 1828, i, p. 521. 

 1836. Delle Chiaje, Instituzione di anatomia comparata, 1836. 



* Leviraia oxyrhynchus, Bonap. — Raia oxyrhynchus, Linn. 



