— 146 — 



an interesting experience in this direction of two herring fishermen, who were fishing 

 with drift-nets in the Great Belt on Sept. 22nd, 1905. It is stated: "Whilst they were 

 casting the lead in 22 fathows of water at 1 a. m., they saw an eel in the water in 

 the light shed by the lantern. On close observation they saw several hundreds 

 go past within the space of an hour (all in the light of the lantern), moving in the 

 direction from east to west under a stiff easterly breeze and strong southerly current. 

 By means of a short-handled landing-net they took 3 specimens. The eels did not 

 pass in a continuous stream but 3—4 at a time, some deep down others right up in 

 the waves." 



It appears from this therefore that the eels in their migration out to the spawning 

 places may at least sometimes travel pelagically and it is very probable that they do so 

 regularly. In this case we should have a very natural explanation of the fact, that the 

 many steam-trawlers which fish in the Kattegat and North Sea seldom or never bring 

 up the eel in their trawls. 



B. The Young Stages of the Eel 



1. The Leptocephali the young forms of eels. The beginning of our present 

 knowledge concerning the developmental history of the eels {Muvaenidœ) may be traced 

 to a treatise published by the German J. V. Carus^ in the year 1861. This deals with 

 a small group of small transparent fishes without reproductive organs which were 

 chiefly known from the Messina Straits and commonly went under the name of Leptoce- 

 phalidae Bonaparte. The relationship of the leptocephalids was however a much disputed 

 point, though they were usually referred as a special group to the fishes without ventral 

 fins 2. Carus then brought forward the theory that the leptocephalids were not adult fishes 

 but merely the larval stages of other species. He was not able to indicate with certainty 

 the species or genera to which the leptocephalid larvae belonged and he expressly states 

 his regret at the end of his paper, that he could only bring forward this negative result, 



' J. V. Carus, Ueber die Leptocephaliden ; Herrn Carl Gustav Carus, Dr. der Philos., Med. u. Chir. etc. etc., 

 zur Feier seines fünfzigjährigen Doctorjubilaeums dargebracht.. Leipzig, Wilh. Engelmann, 1861. The older 

 literature is detailed in Carus' treatise. 



2 The most comprehensive of the older works on the Leptocephali is by Kauf : Catalogue of the Apodal 

 Fish in the British Museum 1856, p. 143 ot seq. in which 22 species described are referred to the four 

 genera: Lepiocepkahis, Hyoprorzis, Tilurus and Esunculus. Of these Esunculus has ventral fins and has 

 thus obviously no right to be placed with the remaining Leptocephali. Hyoprorus is a genus with only 

 I species: H. Messinensis Köll. This species (4'96" long) is remarkable in that the body is strongly compressed 

 and is abruptly enlarged (in height) behind the head. The snout is elongate and there is one continuous ver- 

 tical fin. The genus Tilurus (with 2 species) has a ray-less dorsal fin but no anal fin. The posterior part of 

 the body is extremely lengthened and tapers oflf to a long whip-like tail near the end of which is the anus 

 (cf Plate IX Fig. 3 and 7 where photographs of two forms are given). Finally, there is the principal genus Lep- 

 tocephahis with a leaf-like compressed body; to this genus according to Kaup belonged 18 different species 

 amongst which L. breviroslris as shown in Fig. i. Most of the Lepiocephalus-sptcits came from the Messina 

 .Strait.s, but a number also from tropical seas. In a later work (Ann. and Mag. of Nat. Hist., 3 ser., vol. VI, 

 i860) Kaup describes more species, but at the .same time follows Yarrell in uniting the species L. Spa/ansanii 

 and L. Morrisii given previously as distinct into one with the name L. Morrisii. This was the only species 

 of Leptocephalus which had been found in Europe outside the Mediterranean. 



