4724 Fishes. 



lakes ; and it is easy to see, by their numerous remains in the limestone 

 of Birdiehouse, and in the limestone of other quarters, that they played 

 an important, perhaps the same, part in the economy of the ancient 

 world that they do in this, namely, serving as food to countless shoals 

 of gregarious fishes, which abounded then as now in fresh and marine 

 waters. 



The Entomostraca of the Southern hemisphere differ seemingly 

 from those of the northern ; there also they serve as the food of gre- 

 garious fishes. This was proved by my brother many years ago, in 

 respect of the so-called herring of the Bay of Islands, a gregarious 

 fish abounding in these seas, and living on Entomostraca. 



To the minuteness, and, indeed, microscopic character of the Ento- 

 mostraca, must be ascribed the fact of their having so long escaped 

 the notice of naturalists and others, and causing even distinguished 

 observers to consider their occasional presence in the stomachs of 

 fishes to be merely accidental. 



The largest of the gregarious fishes I have as yet observed which 

 lives, or may live, exclusively on the Entomostraca, is the early gray 

 trout of Loch Leven and the char; but I have no doubt that on the 

 American continent there are many admirable fishes of the natural 

 families of Salmonidae, Corregoni, Clupeadae, and even others, whose 

 food, when discovered, will be found to be Entomostraca of various 

 species. They vary considerably in size, and seem to extend from 

 pole to pole, consuming the organic remains which but for them 

 might speedily infect the ocean itself. 



To the geologist the facts stated in this memoir must, I think, prove 

 of deep interest. Certain of the most productive of the gregarious 

 fishes of past and present times depend for their existence on a class 

 of animals exposed to destruction by chemical or other changes in the 

 waters they inhabit: their destruction would v probably involve the 

 fish which prey on them. As regards the herring, these facts may 

 some day explain the capriciousness in the movements of the vast 

 shoals which visit the coasts of Scotland and other northern 

 countries — their appearance and disappearance at various times; for 

 the question of food must be with herrings, as with men, the all 

 important question. 



R. Knox. 

 M iessen House, Upper Clapton. 



