162 Papers from the Department of Marine Biology. 



electroplaxes are much wider apart than in others. For instance, in 

 Astroscopus there is a distance of 12 microns between every two elec- 

 troplaxes, while in the Rajidfe the distances vary in the different species 

 from 15 to 75 microns. In Torpedo occidentalis there are 5 microns 

 between the electroplaxes, in Torpedo ocellata 4 to 8, and in Gymnoius 

 15; while in the Mormyridse the space is very large. 



EXPERIMENTAL. 



It was hoped at one time that the shock of Astroscopus might be 

 accurately measured and so given its place among the other electric 

 fishes. One Uving specimen was sent from Norfolk, Virginia, to the 

 Princeton aquarium, where, with the aid of a physicist. Professor 

 Adams, of Princeton University, a few experiments were carried on. 

 Unfortunately the specimen was so weak from exhaustion when it 

 arrived that only fatigue phenomena could be observed, and since the 

 specimen never revived it was impossible to measure the current with 

 any accuracy. It was possible, however, to make a few observations 

 of value. The direction of the current was tested and found to agree 

 with Pacini's law (76) — in other words, to pass from the motor to the 

 nutritive layer of the electroplax. With the exception of Malopierurus, 

 all electric fishes examined in this regard have been found to agree with 

 Pacini's law. The exception of Mcdopterurus in this respect is probably 

 not a serious one, since it was already known to differ from other electric 

 fishes in nearly all respects except the power to give electric shocks and 

 in its possession of the characteristic transparent jelly-like areas. 



In Gyfnnotus and Morrtiyrus (Garten 49), where the electric layer is 

 posterior to the nutritive, the current passes from tail to head. In 

 Raja, which has its electric area on the anterior side, the current passes 

 from head to tail. In Torpedo the electric disk is on the ventral side 

 and the current passes from ventral to dorsal, and now it is seen that in 

 Astroscopus the current passes from dorsal to ventral, the electric sur- 

 face being on the dorsal side. No living specimen of Gymnarchus has 

 been obtained, but the general resemblance of the organs of this fish 

 (both in structure and origin) to those of the other Mormyridae leaves 

 very little room for doubt that the current passes from tail to head, as 

 in those fishes. 



The current entering on the dorsal side in Astroscopus makes the 

 dorsal surface negative to the ventral ; the nerve-endings are therefore 

 all on the negative side, .llthough the organs of the various fish are 

 imiervated in quite different ways, yet in every case the entire electric 

 surface is covered with nerve-endings, so that if it be the nerve and not 

 the organ which generates the electricity the amount of electric surface 

 and the arrangement of the surfaces would still be significant. 



