M. Robin on a pecidiar Organ found in the Rays. 21 



of the faces of the apparatus ; but they are more or less contorted, 

 and are interrupted at intervals. The interruptions proceed from 

 the discs becoming at intervals irregular, more narrow, and the 

 series of discs terminates ordinarily in a very small, triangular 

 one. It follows from these anatomical arrangements, that on the 

 surface of the organ we may perceive one of the small faces of 

 each of the superficial discs, and study very regularly the elon- 

 gated, quadrilateral or lozenge-shaped polygonal, sometimes hex- 

 agonal form which it assumes in consequence of the reciprocal 

 pressure which it undergoes from the adjoining discs. We may 

 moreover very easily perceive that when the discs of a series 

 begin to lose their form and are interrupted, there exist at the 

 side other irregular discs which commence a new series. It is to 

 be remarked also that the discs are ranged more regularly on the 

 internal surface of the apparatus in the Raia ruhus and R. batis 

 than in the Raia clavata ; in the first two species we also observe 

 on the internal surface of the organ, that one of the partitions 

 which separates the series of discs on the internal surface, follows 

 its whole length and is of greater thickness than the rest : it is 

 formed by glistening aponeurotic fibres, and it forms a sort of 

 longitudinal pile into which the vessels and the nerves penetrate. 



With respect to the gelatinous substance of the discs, mag- 

 nified 400 diameters, it is seen to be hollowed out by cavities, 

 and the walls of the latter are hollowed by cavities gradually 

 lessening in size. The substance too which circumscribes these 

 areolse (to which we shall recur hereafter) is hyaline, homogeneous 

 and transparent; it is studded with extremely fine molecular 

 granules. From one spot to another are very regular granular 

 spheres of O^^^^'OOSO, surrounded by a very pale circular mass of 

 granules siipilar to the preceding. It is impossible to recognise 

 veritable cellules with walls and nuclei, and it is easy to see that 

 the preceding areolae are not cellules ; we shall soon speak of 

 their uses. On the margins of the discs, the homogeneous gela- 

 tinous substance presents regularly undulated strise which it 

 would be impossible to take for fibres. 



At the point at which we are arrived, it is impossible not to 

 recognise a great analogy between the semitransparent gelatinous 

 substance which essentially constitutes the discs of the peculiar 

 organ of the Rays, and that of the prisms of the apparatus of the 

 Torpedo, the rhomboidal meshes of the Silurus electricus, and 

 those interrupted ones between the transversal and vertical fibrous 

 laminae of the Gymnotus. 



Although there may be differences in form between the discs 

 of the organ of the tail of the Rays and those which constitute 

 the prisms of the electrical apparatus of the Torpedo, these dif- 

 ferences are certainly less considerable than those of the portions 



