648 IfATURAL HISTORY OF AQUATIC ANIMALS. 



after, and to be deposited in other years. It is very hard to understand how young Eels could 

 find room in the body of their mother if they were retained until they had gained any considera- 

 ble size. The eel embryo can live and grow for a very long time supported by the little yolk, but 

 when this is gone it can only obtain food outside of the body of its mother. The following circum- 

 stances lead us to believe that the spawning of the Eel takes place only in the sea: (1) that the 

 male Eel is found only in the sea or brackish water, while female Eels yearly undertake a pilgrim- 

 age from the inland waters to the sea, a circumstance which has been known since the time of 

 Aristotle, and upon the knowledge of which the principal capture of Eels by the use of fixed 

 apparatus is dependent; (2) that the young Eels with the greatest regularity ascend from the sea 

 into the rivers and lakes. 



All statements in opposition to this theory are untenable, since the young Eels never find 

 their way into landlocked ponds in the course of their wanderings, while Eels planted in such 

 isolated bodies of water thrive and grow rapidly but never increase in numbers. Another still 

 more convincing argument is the fact that in lakes which formerly contained many Eels, but 

 which by the erection of impassable weirs have been cut off from the sea, the supply of Eels 

 has diminished, and after a time only scattering individuals, old and of great size, are taken in 

 them. An instance of this sort occurred in Lake Muskendorf, in West Prussia. If an instance 

 of the reproduction of the Eel in fresh water could be found, such occurrences as these would be 

 quite inexplicable. 



In the upper stretches of long rivers the migration of the Eels begins in April or May; in their 

 lower stretches and shorter streams later in the season. In all running waters the eel fishery 

 depends upon the downward migrations. The Eels press up the streams with occasional halts, 

 remaining here and there for short periods, but always make their way above. They appear to 

 make the most progress during dark nights when the water is troubled and stormy, for at this 

 time they are captured in the greatest numbers. It is probable that after the Eels have once 

 returned to the sea, and there deposited their spawn, they never can return into fresh water, but 

 remain there to die. A great migration of grown Eels in spring or summer has never been reported, 

 and it appears certain that all the female Eels which have once found their way to the sea are 

 lost to the fisherman. In No. 8 of the German "Fischerei Zeitung" for 1878, Dr. Schock published 

 certain statements sent to him by Dr. Jacoby. It is remarked in this paper, among other things, 

 that after the deposition of the spawn the female Eel dies a physiological death, and that occasion- 

 ally the sea in the neighborhood of the mouths of rivers has been found covered with dead Flels 

 whose ovaries were empty. When, where, and by whom this observation was made, and ,- ho 

 pronounced upon the empty ovaries in these dead fish, is unfortunately not mentioned. 



A great number of the Eels remain in inland waters while others proceed to the sea, either 

 because their eggs are at this time not sufllciently ripe, or perhaps because they are sterile. It 

 would seem probable that the increase in the size of the eggs in the wandering Eels begins to be 

 very rapid after August and September, while in the earlier months of the year, in all Eels of 

 moderate size, the eggs were at the utmost but about 0.09 millimeters in diameter. In Septem- 

 ber of the same year, I found (as an average of numerous measurements) a diameter of 0.10; in 

 October, 0.16 ; in November, 0.18 to 0.23, while the eggs showed other characters connected with 

 approaching maturity which earlier in the season were not to be seen. All the Eels which were 

 captured later — in December and in January — part of which came from rivers and harbors, part 

 from the harbor of Putzig (Putziger Wiek), had eggs measuring from 0.09 to 0.16 millimeters, 

 although among the fish examined were some which measured three feet in length. 



