146 The Apodes, or Eel-like Fishes 
destined to mature hereafter and 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 considerable size. The eel embryo can live and 
grow for a long time supported by the little yolk, but, when 
this is done, it can only obtain food outside of the body of its 
mother. The following circumstances 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 pilgrimage 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 Musken- 
gorf 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 in 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 
