August nth. ICXJ4 by the h'ish investigation steamer "Helga" off h-eland. Later, in IQ05 

 numerous specimens (several hundreds) were found by the "Thor" to the west of the 

 British Isles and France over depths greater than ca. 1000 meters. That our specimens 

 really belong to the common eel (A. vulgaris) is proved by the facts: (i)that the 100 

 specimens examined had the same number of vertebrae as this species, and (2) that all the 

 transition stages between L. brev/rosiris and cylindrical eel young were found. 



Of all the regions investigated by the "Thor" in 1905 the area off the English Channel 

 was the one where by far the most eel larvae were found, namely, up to 70 specimens 

 per haul (of 2 hours). Large masses of eels obviously spawn here and the region off 

 the English Channel must be regarded as the most northerly of the main spawning places 

 of the eel in the Atlantic'. 



The larvae of the eel {Leptocephahis brevirostris) are true pelagic animals as is 

 shown by their whole organisation. They have consequently nothing whatsoever to do 

 with the bottom and do not pass their life buried in the bottom as some have formerly 

 believed. In the living condition they are quite clear and transparent like glass and are 

 always found in company with other forms just as distinctly pelagic, amongst which 

 salpae, pteropods (e. g. Cymbulia and Hyalaed) and glas-clear heteropods {Carinaria) 

 and Crustacea {Phronimä) deserve special mention. They are further accompanied by 

 various pelagic fish young, amongst which are first of all 5 other Leptocephali (the larval 

 forms of Synaphobranchits ■pinnatus and Conger vulgaris chiefly) but also the young 

 of many different fishes, both pelagic and deep-water forms. 



The larvae of the eel {L. brevirostris) must therefore be considered as true pelagic 

 deep-sea forms, and this applies also to the other Leptocephalus species taken by the 

 "Thor". What the conditions are in the stages preceding the Leptocephalus (preleptoce- 

 phalic stages) has not yet been determined. 



Leptocephahis brevirostris occurs chiefly in the upper and middle water 

 layers, where it is found close to the surface but in greatest numbers at a depth of 

 about 100 meters (in the day). Like many other pelagic fishes it seems however to rise 

 higher up in the water at night than in the day. Its movements are not specially rapid, 

 eel-like and undulatory, and it is often seen to remain quite still in the water. 



As mentioned, the appearance of the still earlier stages of the eel is not known, as 

 neither the eggs nor the preleptocephalic larval stages have been found or at least 

 identified. It is known that the eels have pelagic eggs. Further the "Thor" has aided 

 us to show that masses of large, pelagic eggs of deep water fishes occur in 

 the Atlantic. These eggs, some of which greatly resemble those of the eels but which 

 belong to the deep water salmonoid Argejitina silus, remain floating in deep water and 

 hatch out there to larvae without normally rising up to the surface (bathypelagic eggs). 

 It is therefore very reasonable to assume that the preleptocephalic stages of the common 

 eel and of many other eel species are normally bathypelagic, and this explains in a natural 

 manner why the preleptocephalic stages do not occur in the rich collections of Leptoce- 

 phali from the surface of tropical seas, since the larvae only rise up to the surface after 

 the preleptocephalic stage of feeding and growth has been passed through. In agreement 

 with this is the fact, that the lower limit to the developmental series of the tropical 



■ A.S to the conditions further to the south see Note p. 256. 



33 



