222 



SALMONID^ OP BRITAIN. 



Teeth. — Of moderate strength, and which it has been asserted exist in this 

 form on the vomer in a single series, and persistent throughout life, but in a 

 double row in burn trout of the same size, but we have first to consider whether 

 the facts as stated are correct. All trout and salmon (not chars) when young, 

 irrespective of the teeth on the head of the vomer, have (as has been already 

 remarked) a double row along its body, but these in all, dependent on age or 

 rapidity of growth, fall out, commencing behind and extending forwards. In 

 salmon and sea trout, which are forms which grow most rapidly, these teeth are 

 shed the earliest, while the Lochleven trout, which is likewise a rapid grower, 

 loses them "rather sooner than the burn or loch form, while to say that in the 

 mature they are invariably in a single row is erroneous. At the same time it is 

 not here advanced that rapidity of growth is the sole cause of this, but the 

 deciduousness of the teeth appears to be owing to the absorption or narrowing of 

 the tooth-bearing ridge on the vomer, in consequence of which, first from being in 

 pairs, they become in a single row and finally fall out. (See fig. 45, page 197 ante.) 



In the following seven specimens of Lochleven trout the condition of the 

 vomerine dental system was as follows : — In a female 20 inches long, 2 teeth 

 exist on the hind edge of the head of the vomer, and 3 along the front half of its 

 body, the two first of which are almost opposite one another. (2) In a male 

 9 inches long, 2 teeth at hind edge of vomer, 2 at the front end of the body, and 7 

 in an irregular zigzag line, almost in one continuous row, while their points turn 



Fig. 50. Outlines, life size, of tail fins of Lochleven trout reared in ponds at 

 Howietoun. 1, at 2 months old : 2 and 3, at 13 months : 4, male, 16 months : 6, 6, 7, 

 males, at 30 months. From specimens in the British Museum collection : 8, female, 

 12 in. long : 9, female, 13 in. long : 10, female, 13'8 in. long : 11, female, 15'4 in. long : 

 12, male, 17 in. long. From Howietoun fish : 13, female, 7 years old, 227 in. long : 14, 

 male, 7 years old, 22 in. long. 



