the sea to the fresh water, at any rate in colder regions where the temperature of the 

 sea-water in winter or early spring is often higher than that of the fresh water'. The 

 matter may in my opinion be considered in the following manner : the eel-fry arrive on 

 the coasts at a time which is chiefly determined by the distance of the place from the 

 spawning places of the eel. After their arrival on the coasts they may if the weather is 

 cold remain in the sea a shorter or longer period, and later, when the weather has 

 become milder and the temperature of the fresh water rises they begin to ascend. 



We have now gradually come so far that a connected biological explanation of the 

 phenomena of the migration to the coasts of North Europe can be attempted. 



Most of the eel-larvae are in autumn about November transformed to glass-eels 

 (Stage 5), which are migrating in towards the coasts from the great depths over which 

 they have lived pelagically. At this period the small eels have become swift and strong 

 in their movements, and from now on their endeavours are to reach in to the coasts 

 where they are specially attracted by outpouring fresh water. 



As we have been able to find the Leptocephali regularly right from the northernmost 

 parts of Scotland to the Bay of Biscay, it seems probable that the eel regularly spawns 

 over that distance, but there is no doubt on the other hand that specially large spawning 

 places where specially large quantities of young are produced lie to the south and south- 

 west of Ireland off the mouth of the English Channel. The easterly and northeasterly 

 migration, towards the coasts is favoured by the main direction of the current, as the eel- 

 fry travel pelagically in the upper water-layers. Quantities of eel-fry move eastwards from 

 the large spawning places south-west and south of Ireland, and the great mass undoubt- 

 edly passed along the south coast of Ireland, which has no great bays or rivers and has 

 further an almost straight east to west direction. The next country they then reach is 

 the south-west of England with the Bristol Channel, which by reason of its 

 whole form and situation must act like the arms of a trap or similar apparatus 

 directly placed for the capture of the elvers coming on from the spawning places. In this 

 way we obtain the biological explanation of the appearance of the colossal masses of elvers 

 in the innermost parts of the apparatus, i. e. top of the Bristol Channel on the Severn 

 River, where millions upon millions are fished by the people. 



A very large number of elvers perhaps especially those which come from places more 

 to the south (Bay of Biscay) manage however to slip past Ushant and Land's End and 

 are carried up the English Channel. In the Channel many of them get a landing on the 

 coasts of England and France, whilst others are carried further into the North Sea. The 

 most undoubtedly succeed here in entering into one or another river on the North Sea 

 coasts of England or the Continent, but some are still carried by the current or other 

 cause out into the central part of the North Sea, where a few are to be found right 

 to the end of April or even somewhat later, living pelagically at least by night. 



I In the Danish waters (e. g. Sound) tiny eel-fry are found in the sea even from the beginning of March 

 (or perhaps a little before), but the ascent into fresh water has not been seen earlier than April. This is possibly 

 due partly to the ascent only being observed when it has reached a certain magnitude. It is also very probable 

 however, that the eel-fry remain so long in the sea because of the higher temperature there, thus for example 

 in the Sound where in early spring it is relatively considerable in the deeper channels. 



