( 467 ) 



XII.— The Lateral Sense Organs of Elasmobranchs : The Ampullary Canals of 

 the Genus Raia. By Augusta Lamont, B.Sc, Baxter Scholar in Natural 

 Science, University of Edinburgh. Communicated by Professor J. C. Ewart. 

 (With Eight Plates and Nine Text-figures.) 



(MS. received July 5, 1915. Read July 5, 1915. Issued separately January 15, 1916.) 



CONTENTS. 



PAGE 



1. Introductory 467 



2. Historical 468 



3. General Characters and Distribution of the 



Ampullary Canals 473 



PAGE 



4. Distinguishing Features of the System in the 



Several Species 480 



5. Innervation ....... 484 



6. Comparison with other Members of the Batoidei 489 



7. Bibliography 490 



1. Introductory. 



For two centuries and a half the ampullary canal system of Elasmobranch fishes 

 has occupied the attention of a series of investigators, who have treated the subject 

 from a variety of standpoints, and have amassed a considerable literature represent- 

 ing, in spite of repetition and some conflicting statements, a gradual advance to a 

 fuller knowledge regarding the occurrence and the structure of the organs in 

 question. 



Early researches suffered from the want of recognition of any distinction between 

 the sensory canal system and the ampullary canal system, both being included under 

 the. term "mucous canals," a name given on account of the secretory function which 

 was ascribed to them. Later, electricity-producing and sensory functions were in 

 turn attributed to them, and the disputed point of their physiology became one of 

 the chief points of interest among the investigators of the first half of the nineteenth 

 century. From the middle of the nineteenth century onwards, the histology and 

 innervation of the ampullae and their canals attracted attention, and as a result 

 these gradually came to be recognised as organs of sense. 



In spite, however, of continuous work and varied treatment, no one among this 

 series of investigators has undertaken to give a complete description of the ampullary 

 canals in any one genus, observations having been made in turn on Torpedo, some 

 species of Raia, Scyllium, Acanthias, Pristiurus, and others. It has therefore been 

 the purpose of the present investigation to attempt what has hitherto been omitted, 

 and to describe as fully as possible one genus — the genus Raia, — comparing with 

 one another as many species of the genus as have been available. 



The present paper gives an account of the general anatomy of the ampullary 

 canal system, based on work which has been carried out in the Zoology Department 

 of the University of Edinburgh. It is hoped that later an account of the histology 

 of the ampullae may be contributed. 



TRANS. ROY. SOC. EDIN , VOL. LI, PART II (NO. 12). 68 



