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than those of the latter), contain an abundance of Eels of excellent quality. 

 Nor is there any difference whatsoever in the character of the rocks over 

 wliich these several rivers flow ; the mountains are generally composed of 

 crystalline sandstones, the main rivers running with their strike, whilst the 

 tributaries usually cut through them nearly at right angles. Nor can the 

 absence of these fish be accounted for by want of a^Dpropriate food, for Lake 

 Guyon and all the smaller and less rapid streams abound in various species of 

 Galaxias, and in other forms of animal life. 



"VVe are, therefore, driven to conclude, either that migration to the sea is 

 essential to the Eel of this country, and that some physical obstacle exists 

 which prevents its return to the head waters of the river in question ; or that 

 it has been introduced into the river below the rapids (where it is abundant) 

 since the formation of some physical obstacle to its further ascent. 



If the absence of the fish in the upper parts of the river is to be attributed 

 to the existence of a physical obstacle to its ascent, then the line of rapids to 

 which I have referred as occurring some thirty miles below its soiirce must be 

 that obstacle. At this point the valley is very narrow, and the river which 

 there contains a great body of water, has cut a channel nearly forty feet deep 

 and about half a mile in length, through solid rock, along which it flows with 

 great force. Judging, too, from the presence of numerous twirls and whirl- 

 pools, the bottom of these rapids appears to be rocky and uneven, whilst the 

 rock on the sides, and, doubtless on the bottom also, has been highly polished 

 by the attrition of the silt brought down during floods. 



But it may be urged that Eels are well known to breed freely in Europe in 

 fresh water habitats, without attempting to seek the sea, and that during the 

 winter season they manage there to protect themselves from the increased 

 rigour of the temperatiire by burying themselves in mud, or by hiding in 

 holes in the banks of the rivers and ponds. Mr. Yarrell, indeed, expressly 

 cites the Mole, the Wey, and the Longford rivers, and various ponds, as 

 localities in which the Eel is found to breed freely, but from which it does not 

 attempt to reach the sea ; and we may be asked why should not the Eels of 

 this country follow the same habit in the Upper Waiau, assuming that the 

 rapids referred to prevent their ascent of the river 1 The coldness of the 

 water during the winter season would not be sufficient to account for their 

 absence, for Mi\ Yarrell has shown that they are able to endure, without 

 injury, a very rigorous temjDerature, and certainly the winter season of 

 the district in question is not so inclement as that of many parts of 

 England. 



We are, therefoi-e, driv^en back upon the two alternatives mentioned in the 

 earlier part of these observations, and of these two I am disposed to rely upon 

 the first, namely, that while migration to the sea is essential to the Eels 

 of this country, a time arrived at which, although descent was practicable, 



B 



