650 NATURAL HISTORY OF AQUATIC ANIMALS. 



Dr. Pauly's discovery is so interesting that I propose to translate his own account of it. The 

 investigation was made, I believe, in Munich, and the report from which I quote was published in 

 the ''Austro-Hungarian Fishery Gazette," of Vienna, December 23, 1880. Dr. Pauly writes: 



"During the past year I have received from Court-fisherman Knffer a large number of Eels, 

 which I have used in my investigations. The large individuals, all of which came from the lakes 

 of Northern Italy, were females. I received, however, from the same individual, another lot of 

 Eels, consisting of much smaller individuals, weighing from twenty to ninety grams (two- thirds 

 of an ounce to three ounces), also taken in fresh water. At the request of Professor von Siebold, 

 I had paid particular attention to the sexes of the Eels which I was engaged in investigating, 

 and to my great astonishment I found that a large majority of these small Eels (nineteen out of 

 twenty-seven) were males, possessing, instead of the familiar ovaries, the 'Lappenorgan' described 

 by Dr. Syrski. A histological examination of these organs convinced me that the structure of 

 these tissues agreed with that described by Freud. . . . 



" My next inquiry was very naturally concerning the locality whence these Eels had been ob- 

 tained. I learned that Kuffer had received them two years before from Director Ilaack at Hiinin- 

 gen, and, upon questioning Director Haack, learned that they had been brought from a French river, 

 the Sevre nantaise, where they were caught as young fry [montee] at a distance of ten or twelve 

 miles from its mouth, and furthermore were at the time of examination about four years old. The 

 small size of these fish, their age being taken into consideration, satisfied me that they had been 

 reared in captivity, since uncultivated Eels would have been much heavier. The females in this 

 lot of Eels exceeded the males in length and weight, and also exhibited those external characters 

 described by Jacoby as indicating sex. 



"The locality iu the Sevre niortaise where these fish were taken may easily, especially at flood 

 tide, have been within the limits of brackish water ; my observations do not prove, therefore, that 

 male Eels enter fresh water. 



"Dr. Jacoby found male Eels in the lagoons of Comacchio, where the water is brackish. These 

 males must have ascended in the 'mounting' as fry, and probably at the approach of sexual 

 maturity descend with the females to the sea. My investigations and those of Jacoby prove only 

 this: that the young female Eels do not necessarily break away from their parents and from their 

 birthplaces at sea, and entirely alone proceed upon their migrations, while the males scatter through 

 the sea, but that their brothers seem to accompany them part of the way upon their journey. But 

 how far ! Do the males know where pure fresh water begins, and are the fry of different sexes found 

 mingled together only at the river mouths t If we bear iu mind the fact that the male organs had 

 so long escaped discovery, that, on account of their crystal-like transparency, their detection in a 

 fresh Eel is so difficult, etc., may we not admit that past conclusions are probably erroneous, and 

 that although thousands of fresh- water Eels have been studied by different investigators, male Eels 

 may yet be found in our streams, especially when more of the smaller individuals have been 

 examined t" 



Dr. Pauly then discusses the observations of Dr. Hermes, who found eleven per cent, of males 

 among Eels taken at Wittenberge, on the Elbe, about one hundred and twenty miles from the Ger- 

 man Ocean, and no males whatever at Havelberg, twenty or thirty miles higher up the stream, and 

 closes his essay with the following conclusions : " Male Eels undoubtedly ascend the rivers, but the 

 numerical percentage of males to females appears to diminish as one proceeds up the streams." This fact 

 is opposed to the theory proposed by some one that young Eels are at first of undifferentiated sex, 

 and have the tendency under the influence of fresh water to become females, under that of salt 

 water to develop male characters. 



