ELECTRICAL ORGANS IN FISHES. 295 



decussating series, and to afford in certain sections the 

 octahedral form attributed to them by Pacini. He also states 

 that these lenticular alveoli consist of a fibrous membrane, 

 covered by a very fine layer on which the nerves are dis- 

 posed. 



On each side of the tail of the skate (Eaia), partly in con- 

 tact with the skin, but chiefly enveloped in the so-called 

 sacro-lumbalis muscle, is an elongated fusiform mass, which, 

 although its electro-motor power has not yet been experi- 

 mentally determined, nevertheless exhibits all the structural 

 characteristics of an electrical battery. The mass consists of 

 a number of longitudinally and somewhat spirally arranged 

 series of discs ; the series being separated from, and connected 

 to, one another by thicker, the discs by thinner, layers of 

 areolar texture. The discs are somewhat triangular, quad- 

 rangular, or pentangular in form, and are invariably arranged, 

 so that their two large surfaces or faces are directed, the one 

 backwards, the other forwards ; and their three, four, or five 

 smaller surfaces or margins enter into the formation of the 

 surface of the series to which they belong. Of the two large 

 surfaces, the anterior, or that towards the head of the animal, 

 is smooth and slightly convex ; the posterior slightly concave, 

 and presents numerous alveolar depressions of various but 

 graduated sizes, which penetrate two-thirds through the disc, 

 and are separated from one another by corresponding straight 

 or slightly-curved partitions, which diminish in size as they 

 pass off from three or four primary ridges, which radiate from 

 near the centre of the surface, and thus separate the alveoli 

 into larger and smaller elliptical or angular groups. The 

 discs consist of jelly-like dotted or granular nucleated sub- 

 stance ; the granules being arranged in the form of spheroidal 

 shells around clear spaces, in each of which a nucleus is situ- 

 ated. The ultimate ramifications of the vessels and nerves 

 are situated not in but on the two large surfaces or faces of 



