The Origin of the Electric Organs in Astroscopus (Juttatus. 165 



series overcomes the resistance sufficiently to give a very strong shock. 

 In Malojoterurus also the arrangement of the disks is an extensive one, 

 even though not apparentlj^ arranged in either parallel or series, and so 

 is adapted to the high resistance of the water. 



It has been calculated, (Schonlein 83) that the electromotive force in 

 one disk of Raja is 0.03, in Torpedo 0.04, and in Malopterurus may 

 reach as high as 0.45 volt. These results show that aside from the 

 number of electroplaxes there is a specific difference in the power of the in- 

 dividual electroplax. It was most unfortunate that the voltage of Astro- 

 scopes could not be determined, as it might then be possible to explain 

 why Astroscopus, which has as many as 200 electric layers in each organ, 

 arranged in series, and with no apparent resistance, should still have 

 a shock so much weaker than Torpedo, as all reports would indicate. 



The organ of Astroscopus, unlike the other electric organs, is not 

 divided into columns, the diameter of a single electric layer being equal 

 to one-third the diameter of the fish. When a current passes through 

 a copper wire the resistance to the passage of the current is inversely 

 proportional to the diameter of the wire. Therefore, were the diameter 

 of a single electric layer in Astroscopus equal to the sums of the diam- 

 eters of the 450 columns in Torpedo, the amperage of Astroscojyus would 

 be equal to that of Torpedo with only one column. As a matter of fact, 

 the diameter of the organ in Astroscopus is much less than that of the 

 columns in Torpedo, although the exact amount has not been computed. 

 The amperage is therefore low, but the voltage being the sum of the 200 

 electric layers should be a little less than half that of Torpedo ocellata. 

 Since it is known to be less than that, it must be that the qualitative 

 differences in the structure of the electroplaxes themselves may offer 

 various grades of resistance and so account for otherwise inexplicable 

 differences in voltage. Still, the organ of Astroscopus has been meas- 

 ured only in small and much fatigued fishes. 



A comparison of the marine electric fishes demonstrates that with 

 the increase in voltage there is correlated not onl}- an increase in the 

 number of columns and in the electroplaxes in a column, but also a 

 decrease in the width of the electroplaxes and in the area between 

 them. In the fresh- water fishes the same general principles hold, 

 except that in Gymnotus the electroplaxes are onlj^ slightl}^ thinner than 

 in the Mormyridse. The thickness in Mormyrus is 450 microns, in the 

 Rajidae from 300 to 700, and in Gymnotus 200, in contrast to 35 in 

 Astroscopus and 15 in Torpedo. In comparison with the number of the 

 electroplaxes in a column, however, the electroplax in Gymnotus is not a 

 great deal thicker than that of Torpedo, so it is possible that the amount 

 of material may affect the strength of the shock by offering some 

 resistance to the current. 



It has been noted that in the so-called weak electric fishes the nutri- 

 tive layer of the electroplax is very definitely striated, as though it had 



