266 THE FRESH-WATER FISHES OF EUROPE. 



never contains more than fourteen rays. All species have a multitude of 

 pyloric appendages. The eggs are large. The young are generally distin- 

 guished by having dark cross bands ; and in old fish the caudal fin becomes 

 less deeply notched. The lower jaw is longer in males than in females. 



Dr. Giinther remarks on the almost infinite variations of these fishes with 

 age, sex, development of the reproductive organs, food, and the properties 

 of the water they inhabit ; and later observations have thoroughly confirmed 

 these views. Some of the species interbreed, and it is probable that these 

 hybrids mix again with the parent species, increasing the variability. The 

 colour is particularly changeable. The young fish lose their transverse bars 

 with maturity, and the males during and after spawning-time become more 

 brilliantly and variously coloured than the females. 



The water influences the colour in developing tints which harmonise 

 with its character. In clear, rapid rivers Trout acquire dark rounded spots; 

 in large lakes with pebbly bottoms the round spots are replaced by crosses, and 

 the fish are brighter and more silvery. In muddy or peaty pools or lakes, the 

 colour becomes darker ; and, where there is little light, may be almost black ; 

 while in the sea the spots are rarely developed, and the coat acquires a silvery 

 brightness. 



Food rather influences the colour of the flesh than of the skin, though 

 when the fish is in good condition, the skin colour is more uniform and bright 

 than at other times. The pink tint of the flesh has been attributed to the 

 pigments of fresh and salt water Crustacea on which these fishes feed. 



The size depends upon food, and species which are extremely small in small 

 mountain pools, become heavy with abundant food in rivers or lakes. 



The proportions of the different parts of the body vary so much as often to 

 make the identification of species difficult. The snout becomes more pointed 

 and produced at maturity in the male, so that the head increases in length 

 with age, but when the fish is well fed, the relative size of the head is much 

 smaller than when it is badly fed. The fins are also variable, and while the 

 caudal is commonly deeply notched in the young, it becomes truncate in the 

 adult ; and individuals which live in rapid streams have all the fins more 

 rounded than those which live in lakes. The skin, too, in old males, thickens 

 remarkably about the spawning season, so that 'the scales become embedded 

 in it, and invisible. 



But while these external characteristics afford no aid in separating species, 

 Dr. Giinther relies on the following characters: l,the form of the pre-operculum 

 in the adult fish ; 2, the width and strength of the maxillary bone in the adult ; 



3, the size of the teeth, though the pre-maxillary teeth have little value; 



4, the arrangement and permanence of teeth on the vomer; 5, shape of 



