PRESH-WATEB TEOUT— PINS, SCALES, AND CJEOA OF. 199 



this fin is most deTeloped in those taken from running waters.* Ventrals inserted 

 beneath the middle or last third of the base of the dorsal fin. Caudal forked in 

 the very young, emarginate in those of a medium size, becoming square in large 

 examples, or even rounded, as shown in figure 46. While Yarrell (edition 3, 

 p. 281) figured a Thames trout 28 in. long, and 11 lb. weight, in which the hind 

 edge of this fin was slightly rounded. It would also appear that as a general rule 

 the tail fins of trout inhabiting rapid streams are usually more deeply emarginated 

 than in specimens living in more stagnant lakes. 



Fig. 46. Tail fins of brook toout. 1, male, 5-6 in. long, from peat 

 burn. 2, male, 6-2 in. long, from peat burn. 3, female, 6'7 in. long, 

 from same place. 4, male, 8 in. long, Colesbourne. 5, male, 9-6 in. 

 long, Colesbourne. 6, female, 10-6 in. long, Lossie river. 7, female, 

 12 in. long, Elgin. Tails of brook trout from New Zealand : 8, female, 

 ^ natural size : 9, male, 20| in, long, ^ natural size : 10, male, 32^ in. 

 long, J natural size. 



Scales. — From 12 to 15 rows are present between the hind edge of the adipose 

 dorsal fin, in a line passing downwards and forwards to the lateral-line : while 

 about 26 or 27 rows are present between the lateral-line and the base of the ventral 

 fin. As regards the appearance of the scales I have had examples from ten races 

 of fresh- water and sea trout photographed under the microscope for comparison 

 one with another, and likewise examined many more, but the variations were 

 found to be so great, even in those from the same specimens, that nothing would 

 be gained by figuring them. The concentric lines in some of those from the sea 

 trout, sewin, and Lochieven seemed in a few examples to be coarser than in the 

 generality of brook trout. 



GcBcal appendages. — The number present vary considerably as has been already 

 referred to (p. 188 ante), and taking a large number of examples, as a rule trout 

 in the north of the British Isles have more than those in the south. Possibly the 

 number of these appendages will be found under certain circumstances of great 

 value in determining whether the food they can obtain is such that on it they 

 thrive or deteriorate. 



* The following give the result of some of the measurements made. Male, Looh Mulaeh 

 Corrie, 14'6 in. long, peotoral Vf ; female, Looh Ard, 12-8 in. long, 6J ; female, Looh Ard, 10'2 in. 

 long, 6|; female. Loch Ard, 11-9 in. long, 7; male, Looh Ard, 11-6 in, long, 6^; female, 

 Gloucestershire, 10'5 ini long, or 6 in the total length. 



