- 139 — . 



Syrski's observations were later confirmed and amplified by a number of observers in 

 various countries, amongst whom may be mentioned Jacoby (1880, Italy), Hermes (1880, 

 Germany), Robin (1S81, France), Brock (1881, Italy), Ryder (1885, North America), 

 Trybom (Sweden) and others. 



It was only when the definite information, that the eels like other tishes have both 

 females and males (the latter the smaller), had thus been obtained, that the way 

 was cleared for the further understanding of the biology of the eel. 



. 2. Yellow and silver eels. The next step was to bring order into the many and 

 various forms of eels which had gradually been distinguished as different by the fishermen 

 and others all over Europe. How great the confusion was in this regard is shown by 

 the many different names which were in use amongst the people in several countries as 

 well as amongst scientists. To give some notion of this I may mention some of the most 

 common names used in England and Denmark. In England the following were or are 

 distinguished: "broad-nosed eels", "sharp-nosed eels", "Dublin eels", "grig eels", "glut 

 eels", "frog-mouthed eels", "snig eels", "silver eels", "yellow eels", "stick eels", "shunt- 

 lings" etc. etc. ; in Denmark: "Klsepaal", "Gulaal", "Visseaal", "Bredpander", "Bredhoveder", 

 "Prokuratorer", "Solvaal", "Blankaal", "Ruseaal", "Vandreaal", "Gaardaal", etc. etc. 



In former times not only the fishermen but even the scientists distinguished between 

 several forms of eels, which were sometimes described as true different species sometimes 

 as varieties of one species. In Denmark Kröyer (Danmarks Fiske, vol. Ill, p. 616, 

 1846—53) thus formed the three species Anguilla mïgraioria, A. acutirostris and 

 A. latirostris, and in England we find Y.^rrell (British Fishes, vol. II, 1836) giving Angtcilla 

 acuiirostris, A. latirostris and A.mediorostris^ whilst Günther later 1870 (Catal. Fish. 

 Brit. Mus. Vol. VIII) was content with two species, viz. Anguilla latirostris and A. vul- 

 garis. For the separation of the species a number of different characters were used, 

 thus chiefly the form and length of the head, size of the lips and eyes, and position 

 and form of the fins, but we do not find that any true, scientifically exact and critical 

 comparison between the various "species" was carried out. It is also very peculiar, that 

 the young of the eels, known from old times as "montée" or "elvers", were as a rule 

 tacitly ascribed to one of the species, though it might be supposed that the others would 

 also produce young; or again the elvers were simply mentioned under the general 

 designation of Angttilla-gQvwxs without any attempt being made to distinguish the same 

 species as for the old eels. 



Most of the more recent authors (e.g. von Siebold, Dareste, Collett, Moreau, 

 Day, Lilljeborg etc.) give however only one European species of eel, Angîiilla vzilgaris, 

 but they do not explain what all the actually existing forms really mean in biological 

 regard, that is, in what relation they stand to one another. 



The first step towards such a biological explanation was made by the Danish solicitor 

 Leth^, who examined a number of eels at different times of the year, both the yellow 

 eels which occur the whole year round and were generally considered as stationary, and 

 the silver eels which wander out from the fresh water to the sea, presumably to spawn, 



I We find the same three species in CouCH and also a fourth : "Dublin eel" (Anguilla hibernicd). (Couch, 

 Fishes of the Brit. Islands, vol. IV, 1865, p. 328). 



~ F. H. T. Leth, lagttagelser over Aalen (Fiskeritidende, 1882, p. 392), 



l8* 



