38 RESULTS OF THE ATTEMPTS TO ACCLIMATISE SALMO SALAR. 



writer drew attention to this uncertainty in tlie years 1879* 

 and 1882t. "Writing of the new modification produced in 

 the jirovailing forms of migratory salmonoids acclimatised in 

 the Derwent, he states : " Whether this local form is the 

 result of hybridism, as suggested by Dr. Grunther, or is 

 simply the effects of the differing conditions of a new environ- 

 ment, I am as yet unable to decide — perhaps a good deal may 

 be due to both influences, It is noteworthy, however, that 

 already in New Zealand + and Tasmania the allied species 

 S. /ario var. Ansunii has developed into types which are 

 characteristic of })articular local streams. This variability in 

 relation to environment is very suggestive, and may yet help 

 to explain the trifling variable differences in character often 

 overlappingbetween S.camhricus, S.gallivensis, S.hracliypoma,. 

 and /b'. trutta of Scotch, English, and Irish streams. Characters 

 which may be greatly affected by environment are not to be 

 depended upon, and in the opinion of some authorities in other 

 branches of natural history such differences woidd not be 

 recognised as of specific or even sub-specific rank. The 

 assumption of hybridism is to me extremely imsatisfactory, 

 for the reason that the extreme types steadily perpetuate 

 themselves in European waters, notwithstanding the extra- 

 ordinary facilities among fishes for intercrossing by 

 natural means which probably have existed unrestricted for 



The reasonableness of this opinion has received strong con- 

 firmation subsequently by Dr. Day in his works on " British 

 and Irish Fishes," and " British and Irish Salmouidse," where 

 he actually reduces all the types named to varieties of one 

 species (»S'. trutta). 



It is not an easy matter to tell what characters ai-e of 

 specific value and what are not, even when the fullest infor- 

 mation has been obtained as to the variability of the 

 individuals of a group ; and the greatest living authorities 

 often come to different conclusions. It would be unreason- 

 able, therefore, to expect, in the absence of the fullest know- 

 ledge respecting variation of size, colour, sculpture, distribu- 

 tion, etc., that any author could determine with accuracy 

 those characters which alone should entitle certain 

 fonns to specific rank. Of course, I am aware of tho 

 difference of opinion which existed, and which still exists in 

 a more modified form, with respect to what constitutes a 

 species and what a variety ; but there is now, with few 

 exceptions, sufficient agreement among the leading jthilo- 

 sophical naturalists to leave little room for doubt in cases 



• Mercury, Hobart, Nov, 25, 1879 : + FiMlics of ToHUiania, p. 130, Hobart, 

 1882. X On the Brown Trout introduced into Otaf/o. By W. Arthur, C.E. 

 (TraoH. N.Z. luHt., li<83.) 



