FRESH-WATER TROUT— FINS, SCALES, AND CiECA OF. 199 



this fin is most developed in tliose taken from running waters.* Ventrals inserted 

 Ibeneatli tlie 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 ajipear that as a general rule 

 the tail fins of trout inhabiting rapid streams arc usually more deeply emai'ginated 

 than in specimens living in more stagnant lakes. 



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

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

 from same place. 4, male, 8 in. long, Colesbourne. 5, male, 9-0 in. 

 long, Colesbourne. 6, female, 10-5 in. long, Lossie river. 7, female, 

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

 i natural size : 9, male, 20J in. long, J natural size : 10, male, 32i in. 

 long, ^ 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, scwin, and Lochleven seemed in a few examples to be coarser than in the 

 generality of brook trout. 



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

 refeiTod to (p. 188 ante), and taking a largo number of examples, as a i-ule 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 circamstances 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 niaJc. Male, Loeh Mulach 

 Corrie, 14-6 in. long, pectoral 7 J ; female. Loch Ard, 12-8 in. long, GJ; female, Loch Ard, 102 in. 

 long, Gf ; female. Loch Ard, 11-9 in. long, 7 ; male, Loch Ard, ll'o in. long, Gi ; female, 

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



