EELS. 273 



The generality of writers on this subject state 

 that eels perform two migrations every year, one 

 during autumn towards the sea, another in spring 

 or early summer from it. It is the adult eels 

 which perform the autumnal journey, for the pur- 

 pose, it is believed, of depositing their spawn (and 

 it is the opinion of many that these never again 

 return up the rivers), while the spring migration 

 seems to be confined to the smallest eels. " The 

 passage of countless hundreds of young eels has 

 been seen and described as occurring in the Thames, 

 the Severn, the Parrett, the Dee,' and the Ban. 

 I am, however, of opinion that the passage of adult 

 eels to the sea, or rather to the brackish water of 

 the estuary, is an exercise of choice and not a 

 matter of necessity, and that the parent eels return 

 up the river as well as the fry. All authors agree 

 that eels are extremely averse to cold. There are 

 no eels in the arctic regions, none in the rivers 

 of Siberia, the Wolga, the Danube, or any of its 

 tributary streams ; yet the rivers of the southern 

 parts of Europe produce four species. There is 

 no doubt that fishes in general, and eels in parti- 

 cular, are able to appreciate even minute alterations 

 in the temperature of the water they inhabit. The 

 mixed water they seek to remain in during the colder 

 months of the year is of a higher temperature than 

 the pure fresh water of the river, or that of the sea. 

 It is a well known law of chemistry, that when two 

 fluids of different densities come in contact, the tem- 

 perature of the mixture is elevated for a time in pro- 

 portion to the difference in density of the two fluids, 



