8o SALMONIDyE. 



the Graylingr, and the Sparling-, or Smelt. But it is only in the first sub-generic group 

 {Salmo)ies) that we meet with such infinite variations as to cause the difficulties alluded to ; 

 these variations are dependent on age, sex, and sexual development, and the properties of 

 the water, as Giinther has remarked. There is, however, another fact in the history of some 

 of them which serves still further to increase complications, and that is that some of these 

 Salmonoids interbreed. 



As to points of variation we find that there is great difference in the colouration between 

 the different individuals of the same species. Again, colouration varies in the same individual, 

 according^ to age and sexual development ; thus the young of the Salmon, as indeed of all 

 the Salvionidcc perhaps, are striped transversely with dark bars ; the colour of a male or a 

 female Salmon in the spawning season (November, December,) is often adorned with various 

 tints of red, yellow, and blue, totally unlike the colouration of the same fish earlier in the 

 year with its bright silver}^ scales. "Nimium ne crede colori" must ever be remembered, 

 because colour rarely assists in distinguishing a species, there being- perhaps not one which 

 has the same colour at all periods of its life. 



The size of some of the Salmonida is subject to variation ; and this depends mainly, if 

 not entirely, on the amount of food to be obtained. I have seen a Trout two years old, 

 taken out of a fair-sized piece of water where food was abundant, which weighed nearh" 

 three-quarters of a pound ; whereas another individual of the same age, which had lived in 

 a small pond with many other Trout for the same length of time and wnth little food, would 

 weigh not more than two ounces and a half. 



Structural variation occurs in the snout in a most marked degree. The long pointed 

 snout of a male ready to spawn is different from that organ before the milt is matured; 

 so in the form of the mandible or lower jaw, which in the breeding- season is generally 

 bent upwards, there is great difference. The tail, moreover, is subject to variation ; in young 

 specimens, in the parr state, that organ is always more or less deeply incised in all the 

 species of Salvio ; in the grilse state the tail is still incised, but not so deeply as in the 

 parr state, whilst in a full grown Salmon the tail is almost square ; so that here we should 

 follow a very fallacious guide did we fail to remember that variation occurs relating to the 

 age and the sexual development of the fish. But not only is the caudal fin thus liable to 

 structural variation ; we are assured by Dr. Giinther that the form and length of all the fins 

 may vary. Species inhabiting rapid streams, as well as still waters, show considerable 

 variations; "those individuals which live in rapid streams, being in almost constant motion, 

 and wearing off the delicate extremities of the fins, have the fin rays comparatively shorter 

 and stouter, and the fins of a more rounded form, particularly at the corners, than individuals 

 inhabiting ponds or lakes ; moreover, one and the same individual may pass a part of its 

 life in a lake, and enter a river at certain periods, thus changing the form of its fins almost 

 periodically." — (P. 5.) 



In the texture of the surface of the body variation occurs. In old males the epidermis 

 is always tough during the spawning season, the scales are more or less deeply imbedded 

 in the skin, and therefore not easily deciduous ; this is not the case at other seasons of the 

 year. 



Thus it will be seen that in all these instances of variation, whether in colouration or 

 in structure, it would be unsafe to depend on them as guides in discriminating species, 

 because such characters are not constant ; they are variable according to the age and sexual 

 development of the fish. But it may be asked, have we no reliable guides on which to 

 depend? Are there no constant characters? Dr. Giinther draws attention to the following 

 points upon which, he thinks, the chief stress should be made in discriminating species. 



I. "The form of the prseoperculum of the adult fish." This will be readily seen by 

 the subjoined woodcut, a is the prseoperculum of the Sewen (S. cambricus), which at a* has 



