ANATOMY OF THE PAEE. 89 



But circumstances necessarily render the characteristics of 

 dentition inapplicable in the case of the parr. For, 1st., it 

 seems all but certain that the smolt and parr have a dentition 

 neither resembling the adult trout nor adult salmon, but uniting 

 the features of both : a type of itself. 2nd. The dentition is 

 a characteristic not altogether to be depended on, not from any 

 error in itself, but from the want of extended research.* 



Anxious to investigate the subject of the dentition of the parr 

 and of the smolt, I wrote to my friend, Mr. Young, of Invershin, 

 to furnish me with a few. The results will be given below. 



II. For obvious reasons, the characteristics of species derived 

 from the strength of the head and jaws, of the respiratory appa- 

 ratus, or gills and gill-covers, and of the locomotive organs, the 

 fins, are much less distinct, much less to be depended on, in the 

 young and imperfectly developed animal than in the adult. In 

 this direction, therefore, I have not sought for any. The same 

 remark applies to the system of colouration of the surface, which, 

 in the adult, when combined with other natural history cha- 

 racters, and backed by the anatomical history of the animal, 

 furnishes valuable discriminations of species, but in the young 

 or imperfectly grown individuals is of little real value. 



III. The number of spines composing the fins seems to me a 

 means of assisting in the determination of species. Comparing, 

 then,the undoubted parr and smolt, of the same size,taken from the 

 same river, but not at the same time, the result was as follows : 



Perfect. Imperfect. Perfect. Imperfect. 



Pectoral fin Parr 11 3 Smolt 13 



Ventral fin ,,82,, 9 



Caudal fin 17 9 19 12 



Dorsal fin 11 4 10 1 



Analfin 8 3 10 3 



By imperfect ray or spine is meant merely those scarcely 

 annulated rays which do not bifurcate, and do not reach the 

 margin of the fin. The others bifurcate. The memorandum 

 giving the above details adds other particulars. The speci- 

 men was a male, and the spleen measured 1^ by f . I think 



* See the chapter on the dentition of the Salmonidse. 



