DR. DAVY ON THE TORPEDO. 540 



put aside by referring- torpedinal electricity to animal secretion, the cause and nature 

 of which are still a mystery *. 



The third opinion may be indulged in as an hypothesis, and, as a guide to research, 

 it may not be useless. It applies, however, almost as much to other varieties of elec- 

 tricity as to that of the Torpedo ; all of which, it is possible, may be compounded, or 

 owe their various effects to the union of several powers or ethereal fluids, and their 

 peculiarities, compared one with another, to the predominance in various degrees of 

 these fluids. What is known of the solar ray is not unfavourable to such an opinion ; 

 and the history of physical science, in relation to elementary ponderable matter, may 

 rather give encouragement to the notion. 



Malta, 

 March 4th, 1834. 



Explanation of the VhkT^s. 



Plate XXII. 



The figures in this plate are intended to show the progress of the embryo, the 

 increase and decrease of the branchial filaments, and the decrease of the external and 

 increase of the internal yolk-vesicle. 



Fig. 1. Foetal Torpedo and yolk-bag, at the period when tlie branchial filaments 



are very short, and do not carry red blood. 

 Fig. 2. Foetal Torpedo and yolk-bag, at the period when the branchial filaments 



are beginning to carry red blood. 

 Fig. 3. Front view of the foetal Torpedo, with the yolk-bag, showing the further 

 increase of the branchial filaments, and the commencement of the deve- 

 lopment of the electrical organs. 



* In examining the structure of the Torpedo, I have found that the skin covering the electrical organs above 

 is not only more coloured, but also thicker than below, and more vascular, and surrounded by more powerful 

 muscles, and supplied with a greater quantity of mucus ; whilst the under surface appears to have a larger pro- 

 portion of subcutaneous nerves. This difference of structure in the two surfaces of the electrical organs is 

 probably somehow connected with their opposite electrical states. 



I may here notice another peculiarity of organization common to both species of Torpedo, which came under 

 my observation in seeking, though unsuccessfully, for the great sympathetic or the analogous ganglionic nerves, 

 which CuviER asserts exist in the cartilaginous fish (Histoire Naturelle de Poissons, tom. i. p. 438,). The pe- 

 culiarity alluded to is represented by Plate XXIV. fig. 5. It has very much the appearance of a nervous gan- 

 glion, but is in reality a blood-vessel, enlarged into a little bulb, lined with a reddish substance like muscular 

 fibre, giving the idea of a small heart. It is situated one on each side of the aorta, from whence it proceeds, 

 just below the great plexus of nerves which supplies the pectoral fin ; and the arterial branch derived from it is 

 lost in this fin. If it be muscular, as it appears, its function maybe to aid in propelling the blood into the pec- 

 toral fin, and perhaps into the electrical organ. 



MDCCCXXXIV. 4 B 



