TRANSACTIONS OF THE SECTIONS. 447 



structure, and peculiarities of the sexual organs are described, 

 and the author gives a statement, from his own examinations, 

 of the dates at which eels in various ponds and rivers in 

 different southern counties deposited their ova and milt, all 

 of which occurred between the 15th of April and the 7th of 

 May. 



The migration of adult eels in autumn, in tide rivers, is con- 

 sidered as extending to the brackish water only, and believed 

 to be induced by the higher degree of temperature there exist- 

 ing. The mixed water is shown by experiment to maintain a 

 temperature two degrees higher than the pure sea or fresh 

 water, from the combination of two fluids of different densities. 



Eels pass the winter imbedded in mud. 



The return of adult eels is shown by the habits and success 

 of the basket fishermen in rivers within the tide-way, who place 

 the mouths of their eel-pots up stream in autumn, and down 

 stream in the spring. 



The ascent of the fry is described as it occurs in the Thames, 

 the Dee, the Severn, and the Parret. 



Sea water contains a much larger proportion of earthy mat- 

 ter, and in consequence less air, than the water of rivers, and 

 fresh water also yields its oxygen much more rapidly than that 

 of the sea ; the author states his belief that no instance of a 

 freshwater fish going to the sea to deposit its spawn will be 

 found, while more than twenty species of truly marine fishes 

 ascend rivers to deposit their spawn, obtaining thereby, for the 

 vivification of the ova, the assistance afforded by a larger quan- 

 tity of oxygen. 



The restlessness of eels during thunder-storms, when enor- 

 mous quantities are taken, is referred by the author to the high 

 degree of muscular irritability known to exist in all animals pos- 

 sessing a low degi'ee of respiration, with which coexist the 

 power of sustaining privation of air and food, a low animal tem- 

 perature, and great tenacity of life, all of which eels are well 

 known to possess. 



Fishes that swim and take their food near the surface die 

 soon when taken from the water, having a higher degree of re- 

 spiration and less muscular irritability, compared with those that 

 swim near the bottom ; and vice versa. 



The paper concludes with descriptions of the characters 

 which distinguish three different species of British freshwater 

 eels. 



