148 



SALMONID^ OF BRITAIN. 



appear to attain the maximum comparative length at two or three years of age, 

 subsequent to which they somewhat decrease. The caudal fins of large male trout 

 are usually more rounded than in females of the same size on an average among 

 many. In investigating the form of this fin it is evident that emargination, more 

 or less deep, is common to all the various races, and that the depth of that emar- 

 gination decreases with age, while, as a rule, it is shallower in young trout living 

 in fresh water than in the marine races (see p. 13 ante). 



As regards the number of csBcal appendages, which have been advanced as a 

 character which may materially aid in discriminating a species, I have already 

 (p. 22) given reasons against accepting this in respect to our fresh-water trout, 

 and will adduce further evidence under the head of the respective races. 



While it must not be supposed that because British anadromous salmonoids 

 generally possess more csecal appendages than are normally found in our indi- 

 genous and so-called non-migratory trout, that such is everywhere the case. It 

 seems that forms in some large lakes have them in great numbers : thus the 

 Salmo marsiUi, from the lakes in Upper Austria, has up to 100; 8. lacustris, 

 from Lake Constance, which Siebold considers the same species, has up to 74. 

 S. venernensis, Giinther, from Sweden, which Malm gives, I believe, correctly, as 

 a variety of the common brook trout, has at least 62, while our larger forms of 

 lake-trout, 8. ferox, have been found possessing a few in excess of those which 

 inhabit streams. 



PBAI'T-NET BWa HAUIiED OH SHOME, 



