288 THE RIVER-SIDE NATURALIST. 



in vast numbers every spring from the estuaries there 

 can be no doubt, and when very minute, will run up every 

 watercourse, however small, and so reach the head-waters. 

 When eels migrate down to the sea they will use any 

 ditch or watercourse for their purpose, even travel long 

 distances over wet meadows. Seeing small eels in fresh- 

 waters is no proof of their having been bred there. 



The late Dr. Francis Day read a paper on the Mode of 

 Propagation of the Common Eel at the annual meeting of 

 the Cotteswold Naturalist Club, May 1886, in which he 

 says : " For the generation of eels, it would seem, so far 

 as we are at present aware, that the presence of salt 

 water is a necessity ; for it has been observed that when 

 these fish leave rivers and brackish waters for the sea, 

 their productive organs have scarcely begun to develop. 

 But their maturing in the sea must be rapid, because in 

 five or six weeks they have arrived at a breeding condition. 

 This rapidity of maturing in the breeding organs would 

 seem to be a cause of extreme exhaustion ; consequently, 

 after the breeding season is over they die, similarly to 

 lampreys and several other piscine forms ; and this 

 furnishes the explanation why subsequent to this period 

 old eels are not observed reascending rivers." This, how- 

 ever, is not to be taken as proved. We should much like 

 to know if dead river eels have ever been found in large 

 quantities either in the sea or in the estuaries. Buckland's 

 hypothesis, as stated above, is much more likely to be the 

 case. 



Eels were by the earlier naturalists supposed to be 

 viviparous and hermaphrodite, but such is not the case. 

 Eels breed like other fish ; both sexes are distinct, and the 

 female deposits its spawn in the brackish waters of the 

 estuaries. Gyrski was the first to discover, in 1873, the 

 milt organs in the male eel, which lie under the two fatty 

 folds which are found in all eels, and appear as a very 

 narrow light band on either side of the vertebral column, 

 and are so glass-like and transparent as to be difficult to 

 make out except when held in an oblique direction towards 

 the sun ; and Day remarks that for the proper propagation 



