216 Papers from the Department of Marine Biology. 



(fig. 24, pi. 6). It should be noted that the brain lies midway between 

 the two portions of the electric tissue in which the electromotive force 

 is generated, and in a transverse section taken across the body of the 

 animal as seen in figure 25, plate 6, we get a better view of this relation 

 of the brain to the electric organ. 



The two poles of the organ, which is possibly some form of multiple 

 concentration cell, are + or anode on the upper or dorsal surface of the 

 animal and or kathode on the lower or ventral surface. First 

 Cavendish and later DuBois-Reymond worked out the course of the 

 current caused by this organ in the surrounding salt water at the time 

 of discharge, and the diagram by Cavendish, as well as the later and 

 more correct diagram of DuBois-Reymond, are shown in text-figures 1 

 and 2, respectively, where the field and its currents at the time of 

 discharge are plotted. It can here be seen that the brain is theoreti- 

 cally lying in a current of some force running from the anode above 

 to the kathode below, outside of the electric organ. These theoretical 

 considerations have been proved to be true practically, by experiments 

 in the laboratory conducted by the same great investigator, and it can 

 thus be stated that the electric motor nerve-cells, in the so-called 

 electric lobes of the brain, lie in a current that passes from above 

 downward, or in the opposite direction from the current that passes 

 through the tissues of the electric organs themselves. 



A word as to the anatomy and general histological arrangement of 

 the electric motor lobes of the torpedoes will be useful before proceeding. 

 The muscle region which develops into the electric organ of this fish 

 is innervated by fibers that proceed from the anterior or motor areas 

 of the medulla oblongata. Owing, however, to their immense increase 

 in size and the way in which they become massed in two symmetrical 

 oval lobes, the two masses are forced by their growth up through the 

 median wall of the medulla and come to lie in what appears to be a 

 dorsal and sensory position (plate 6, fig. 26). 



All the large cells in this mass, as will be presently described in more 

 detail, have several processes, one of which is the neuraxon or efferent 

 process. This neuraxon leaves the cell and, joining with other neurites 

 from adjacent cells, all pass in these groups toward other similar 

 groups, finally uniting to form the very large nerve-trunks that pass out 

 of the ventro-lateral edge of the nerve-tract to go to the electric organs. 

 Since the neuraxes pass downward on their course they usually leave or 

 emerge from the ventral surface of the cell, but this is not true in all cases. 



It is easy to see from this description and from plate 6, figure 26, 

 and text-figure 6 that the functional polarity or axis of the cell is in a 

 majority of cases dorso- ventral, or, as the fish usually lies, is up and 

 down. But while this is true, a not insignificant number of cells are 

 so placed that, in order to reach the larger general groups of nerve- 

 fibers, their neuraxes must leave them from any of their lateral sur- 

 faces or even from their dorsal or upper surface (text-fig. 5). 



