Arthur. — On the Brown Trout introduced into Otago. 467 



difference iu the productions of the windward and leeward groups, the only 

 possible natural division of the Archipelago." In attempting to throw light 

 upon the remarkable difference in the inhabitants of the different islands, 

 he points out that, as the Archipelago is free, to a most remarkable degree, 

 from gales of wind, neither the birds, insects, nor lighter seeds, would be 

 blown from island to island, and that the profound depth of the ocean 

 between them and their apparently (in a geological sense) recent volcanic 

 origin, rendered it highly unlikely that they were ever united, a considera- 

 tion far more important than any other with respect to the geographical 

 distribution of the inhabitants of the group. 



But although certainly less striking than that of the Gralipagos, the New 

 Zealand case, when carefully examined, and taken with especial reference 

 to the very narrow strait which separates the two islands, and the proba- 

 bility that they were once united, is one of great peculiarity, masked how- 

 ever by the greater extent of the flora, and of the number of orders repre- 

 sented in proportion to the number of genera and species of each. 



Without going more at length into this subject, which might be 

 wearisome, I think I have shown sufficient to excite the attention of 

 naturalists, and to induce such observations as may help us to a clue to the 

 special causes, which, under the law of natural selection, have brought 

 about these remarkable results. 



Art. LV. — On the Brown Trout introduced into Otago. — Paper No. 2. 

 By W. Arthur, C.E. 

 [Read before the Otago Institute, 13th November, 1883.] 

 Plates XLIIL and XLIV. 

 The first paper of this series I read to this Institute in 1878,* and the results 

 of my observations continued since then I now propose to lay before you. 

 My chief object in so doing is to record the effects (if any) consequent on 

 the acclimatization of trout (Salmo fario) in our waters ; on their growth, 

 habits, and structure, as bearing on the theory of the variation of species. 

 Dr. Francis Day, late Inspector-General of Fisheries for India, has made 

 public his investigations on trout in England, — carried out about the same 

 time as my first observations, — and which bear out, to a great extent, the 

 fact that the anatomical distinctions laid down by Dr. Giinther in his cata- 

 logue, between some of the species of Salnionidas, are not altogether to be 

 depended on. Professor Huxley also has recently commenced an examina- 

 tion into the distinguishing marks of the young of the British Salmonidae, — 



* See Trans. N.Z. Inst., vol. xi., art. xxiv. 



