328 Zoological Collections. 



bable; but I know no reason why such mules should always continue 

 small, except that it may be a mark of impregnation. The only difference 

 between the par and the common small trout is in the colour, and in its 

 possessing one or two spines more in the pectoral fin. The par has large 

 blue or olive-bluish marks on the scales, as if they had been made by the im- 

 pression of the fingers of a hand ; and hence the fish is called in some 

 places Fingerlings. The river and sea trout seem capable of changing per- 

 manently their places of residence ; and sea trout seem often to become 

 river trout. In this case they lose their silvery colour, and gain more 

 spots ; and in their offspring these changes are more distinct. Fish like- 

 wise which are ill fed remain small, and pars are exceedingly numerous in 

 those rivers where they are found, which are never separated from the sea 

 by impassable falls ; from which I think it possible that they are produced 

 by a cross between sea and river trout." — Salmonia, p. 66-69. 



2. On the Generation and Migration of Eels. 



The problem of the generation of eels is the most abstruse and one of 

 the most curious in natural history, and though it occupied the attention 

 of Aristotle, and has been taken up by most distinguished naturalists since 

 his time, it is still unsolved. Lacepede indeed asserts, in the most unqua- 

 lified way, that they are viviparous, but he adduces no proofs of his asser- 

 tion. 



There are, it is certain, two migrations of eels, — one up and one down 

 rivers, one from, and the other to the sea, the first in spring and summer, 

 and the second in autumn or early winter. The first of very small eels, 

 which are sometimes not more than 2 or 24 inches long ; the second of 

 large eels, which are sometimes 3 or 4 feet long, and which weigh from 10 

 to 15, or even 20 lbs. There is great reason to believe that all eels found 

 in fresh water are the results of the first migration : they appear in mil- 

 lions in April and May, and sometimes continue to rise as late even as 

 July, and the beginning of August. I remember this was the case in Ire- 

 land in 1823. It had been a cold backward summer, and when I was 

 at Ballyshannon about the end of July, the mouth of the river which had 

 been in flood all this month under the fall was blackened by millions 

 of little eels, about as long as the finger, which were constantly urging 

 their way up the moist rocks by the side of the fall. Thousands died, but 

 their bodies remaining moist served as the ladder for others to make their 

 way ; and I saw others ascending even perpendicular stones, making their 

 road through wet moss, or adhering to some eels that had died in the at- 

 tempt. Such is the energy of these little animals, that they continue to 

 find their way in immense numbers to Loch Erne. The same thing hap- 

 pens at the fall of the Bann, and Loch Neagh is thus peopled with them : 

 Even the mighty fall of Shaffhausen does not prevent them from making 

 their way to the Lake of Constance, where I have seen many very large 

 eels. 



There are eels in the Lake of Neuchatel which communicate by a stream 

 with the Rhine ; but there are none in the Lake of Geneva, because the 



