- 237 — 



I have put together below the places of occurrence of the common eel and of a true 

 Atlantic deep-water eel {Syiiapkohmnclins piiiiiatits) at the different stages of their life, 

 so far as these are known from our investigations with the "Thor". From this we see, 

 that there are considerable resemblances: 



Spawning-period 



Leptocephalus- 

 period 



Metamorphosis- 

 period 



Growth-period 



The common eel 



{Angztil/a vulgaris) 



Deep-water eel from 



the Atlantic Ocean 



(Synaphobraiichiis 



piiinalus) 



Great depths 



do. 



Pelagic in upper 



water layers over 



great depths 



do. 



Comes into shallow 



water along the 



coasts 



Goes down to the 



bottom in great 



depths I 



Shallow water 



Great depths 



If we wish to understand the life-history of the eel it ought undoubtedly to be regarded 

 by the light of the relation of the eel to the other eel fishes. The relation may then 

 be expressed thus: The eel {Anginlla vulgaris) is like most of the other eel 

 species, a true deep-water fish which in its biology only differs from these 

 in that at certain stages of its life, namely the growth-period, it lives, 

 or so far we know, exclusively lives in quite shallow, brackish or fresh 

 water. On account of this peculiar adaptation to a temporary stay in shallow, fresh 

 or brackish water the common eel, in contrast to most of the other eel species comes to 

 have an economical importance for man. 



If we keep in view the two facts: (l) that the eel biologically is a deep-water fish 

 and (2) that is is well-known, that many fish at certain stages of their life, particularly 

 the earlier, live under quite other conditions than during the spawning period, then it 

 appears to me, that the apparently incomprehensible or mysterious in the life-history of 

 the eel must for the most part disappear. Nevertheless we may still wonder at (l)the 

 length and constancy of the migrations many eels, especially those which grow up far 

 from the Atlantic, must undertake and specially at (2) the unusually great differences 

 shown by the outer conditions under which they propagate from those under which they 

 grow up. 



the "Thor's" material of undetermined Leptocephali in order if possible to identify them. The result of his 

 examination wa.s, that one Leptocephalus-sc^oxts, which amongst other characters is distinguished by the lack 

 of pigment and by its very peculiarly shaped telescopic eyes, belonged to Synaphobranchus pinnahts. This 

 Lepiocephalus occurred in large quantities in the upper water-layers together with Leptocephalus brevirosiris 

 and Morrisii. 



I Of this Synaphobra7tchus /z>z;«a/«j- Leptocephalus, which was taken in quantities in June together 

 with Lepiocephalus brevirosiris pelagically in about loo ni. depth, I also took September ist in a deeper 

 haul (i2oo m. wire out) a pelagic specimen, in which the anus had begun to move forward (see fig. 6, PI. IX). 

 On the other hand none were found in September near the surface, where the 2nd^4th Stage of the larvae of 

 the common eel were taken. This observation, which is still an isolated one, seems thus to show, that the 

 Leptocephali belonging to the deep-water eels, when about to metamorphose move down nearer to the bottom 

 than when they are in the true (ist) Leptocephalus-stage, during which they stay nearer the surface like Lep- 

 iocephalus brevirosiris. 



