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nonnal development, namely, the fresh water or at any rate the coasts, where they com- 

 plete their metamorphosis and begin to grow. But all the eel- fry do not succeed 

 in getting inland on the coasts which lie nearest the spawning places. These fry lead 

 a pelagic life completely or partly and thus come under the influence both of the surface- 

 currents in the sea and of the strong winds which may carry them away from the coasts. 

 Many of them therefore do not reach land until they come to the coasts of the North 

 Sea, and others still fewer not even until they pass the Skaw and come into the Danish 

 and Swedish waters. Denmark and the other Baltic countries thus owe their 

 stock of eels to this remainder of the colossal masses of eel-fry migrating 

 from the Atlantic, which from some chance causes do not earlier succeed in getting 

 into the fresh water. These chance causes, e. g. direction and strength of the currents 

 and winds on the way from the Atlantic to the Baltic can naturally, like all other climatic 

 conditions, vary from one year to another, and it will therefore depend on these 

 how many eel-fry in any given year are brought into the Danish and 

 Swedish waters. 



6. Why the eel does not propagate in the neighbourhood of the continental 



coasts of North Europe 



The mystery which so long hung over the developmental history of the eel was 

 for a great part unfolded by the work of Grassi and Calandruccio published about ten 

 years ago. 



It is especially the zoological side of the question, to whose solution the two 

 Italians have contributed in so excellent a manner. The Messina Straits were also un- 

 usually well suited to this purpose, as at few or perhaps no places in the world is there 

 relatively such an easy way of getting the larvae of the eels in quantities throughout a 

 great part of the year as just here. 



On the other hand the Italian authors have not entered so deeply into the biological 

 side of the question. This was quite natural, as their investigations were intended first 

 and foremost to clear up the purely zoological question (of metamorphosis) and chiefly 

 because their investigations were restricted to the Messina Straits. The quite unusual 

 current-conditions there, which on the one hand allow the eel-larvae (Leptocephali) to be 

 so easily obtainable, on the other hand make it difficult to study the normal biology of 

 the eel-larvae at that place. We thus see, for example, that Grassi and Calandruccio 

 did not succeed in determining whether the larvae of the eel in the L. brevirostris stage 

 was normally a bottom form or whether it normally lead a pelagic life. 



In spite of the facts, that the zoological side of the question was so well cleared up by 

 Grassi and Calandruccio and that they were able to determine through experiment and 

 to observe directly, how the Leptocephali changed in aquaria to normal young eels, their 

 investigations were received with no little distrust. This applied both to a great number 

 of scientists and to the general public interested in the "eel-question" round about Europe, 

 for example, not least in Denmark and other North European countries, where the eel 

 plays so great a part in things of common knowledge. The reason for this is however 

 not difficult to see. First and foremost, the discoveries of the Italians tended to completely 

 revolutionise the many prevalent and accepted views of this question, on which the way of 



