THE GYMNOTID EELS OF TROPICAL AMERICA. 165 



Sachs. During one hour this eel gave 150 distinct shocks and by actual measure- 

 ment the last was as strong as the first. Humboldt stated that after a few shocks 

 the eel became exhausted and it took both food and rest to recuperate its electric 

 power. Sachs found no evidence of such a condition. 



The shock of the electric eel readily decomposes potassium iodide, as has 

 been shown by its effect on potassium iodide starch-paper. 



3. Origin of Electric Organs. 



Fritsch concluded (Sachs' Zitteraal, 355 et seq.), after a comparison of the 

 musculature of electric eels and the other Gymnotids, that the large electric organs 

 have originated through the metamorphosis of the lateralis imus muscles. This 

 view is substantiated in several ways. The muscle lateralis imus occurs on both 

 sides of the median line in the other Gymnotids in precisely the position occupied 

 by the large electric organs in the electric eel, in which this pair of muscles are 

 wanting. Along the ventral side of each of the large electric organs is a small strip 

 of muscular tissue, which is continuous with the electric plates. This is probably 

 an unmetamorp hosed remnant of the muscle lateralis imus. The origin of Hunter's 

 and Sachs' organs has not been definitely worked out. The remaining musculature 

 is the same in all Gymnotids. It is known that the electric organs of several of the 

 other electric fishes (Torpedo, Malopterus, etc.) are metamori^hosed muscle tissue. 



II. Eigenmannia virescens (Valenciennes). 



Sachs {I. c, p. 69) recorded in his notes an observation on pseudo-electric or 

 electric tissue in Sternopygus (Eigenmannia) virescens. As this i^ortion of the 

 notes was not worked up before his death it is not clearly understood. He wrote: 



"Der dem electrischen Organ von Gymnotus entsprechende Theil zeichnet 

 sich durch regelmassige Streifung in Zwischenraumen von 1 ""■ aus. Der Durch- 

 schnitt hat ein entschieden an Gymnotus erinnerndes Verhalten. Die betreffende 

 Stelle (a) ist durchscheinend und von horizontalen Septis durchzogen, Die mikro- 

 skopische Untersuchung fallt wegen der Schwierigkeit des Gegenstandes unge- 

 ntigend aus. Es werden jedoch Formelemente, etwa ahnlich dem Durchschnitt 

 der Flatten von Malopterurus, mit runden Kernen und einfach buchend, nach- 

 gewissen. Andererseits finden sich gewaltige Mengen dicker markhaltiger Nerven- 

 fasern mit reichen btischelformigen Verzweigungen. Der Zusammenhang der 

 (etwaigen) beiden Elemente aufzuklaren gelingt aber nicht in befriedigendcr 

 Weise." 



This is accompanied by a figure which is reproduced in Plate XIX, Fig. 24. 

 Fritsch, after a careful examination of specimens of this species, doubts the existence 

 of these elements. The region marked "a" by Sachs was occupied, in the speci- 

 mens I examined, by connective tissue fibers and the edge of the two lateralis 

 muscles. Eigeiimannia virescejis is the only other Gymnotid besides E. electricus to 

 which electric tissue has been ascribed. 



