Ji02 Mil. F. DAT ON BlUTISH SALMON'ES. 



- The foregoing results threw strong doubts upou the validity, 

 first, of hoAv the species had been subdivided, and, secondly, as to 

 their distribution ; while, if the number of vertebrae in all the 

 seven forms of non-migratory freshwater trout inhabiting our 

 islands merely varies between 56 and 60, 1 possess examples from 

 one locality (Cardiganshire) in which they differed from 57 to 

 60, and in an example of the same variety from Penzance I have 

 only found 56. Dr. Cobbold likewise gives an instance of a 

 Scotch trout (S.fario) that he examined, and which had only 56 

 vertebrae. It is evident that too much stress has been attached 

 to the number of vertebrae in trout ; and no confidence can be 

 placed on such as affording evidence of specific difference. 



We thus arrive at the remarkable fact that the form considered 

 by Dr. Giinther as S.fario may possess from 56 to 60 vertebrae, 

 which are exactly the extreme limits he ascertained existed 

 among all the freshwater non-migratory trout of the British Isles. 



Then, as to the number of these bones which are present, some 

 other facts should not be overlooked. This family of fish is 

 exceedingly prone to affections of the spinal column. Occa- 

 sionally two small vertebrae take the place of one large one, as if 

 a division had occurred ; while in others may be observed an 

 abnormally large one, as if two had coalesced, as shown by the 

 normal number of haemal spines for two vertebrae being present. 

 Dr. Griinther, in Ins interesting volume, even instances a case 

 "Avhere three vertebrae were united." 



The number of c^cal appendages has been adduced as a cha- 

 racter Avhich may materially assist in fixing a species ; and if 

 unexpected variations occur, their cause, it is asserted, may be 

 found in the partial confluence of the caeca. Dr. Griinther gives 

 the extreme limits of variation in his six species of non-migratory 

 freshwater trout (excluding the Loch-Leven) as being between 

 33 and 50. But it appears to me that the diflSculty does not 

 appear so much in discovering variations, as in determining 

 within what fixed number they exist in a given form : thus in 

 Grloucestershire I found them at least from 84 to 39, and in 

 Cardiganshire from 35 to 44. The question first requiring 

 solution is, whether the number of these appendages is per- 

 sistent or inconstant, and Avhether change of climate and food 

 may occasion any variation. 



I must here refer to the Tasmanian experiment, wherein it 

 appears that the common brook-trout of the Thames and the 



