GREAT BRITAIN. H 



the character of the water they inhabit, for if the latter is 

 opaque and muddy, its finny inhabitants are found to be 

 darker than are those obtained from localities where it is 

 clear ; in running streams they are generally lighter and 

 brighter than when from stagnant pools, and the same 

 difference may be observed between such as are taken in 

 the open sea or along a muddy coast. 



Age and season likewise exercise an influence in this 

 respect, as well as the health of the fish and temporary 

 emotions. In the very young, one sees but few markings 

 or colours, but these rapidly develop themselves, and by 

 the time, or even before, the first breeding season has been 

 reached, the brilliancy of the individual has often attained 

 to its maximum. Many see in these markings grounds for 

 assuming the probability of the descent of many forms 

 from some common ancestor ; thus vertical bands are almost 

 invariably among the young of all the salmonidse, as well as 

 in most of the marine scombresocidae, in which they are 

 generally diagnostic of the immaturity of the individual. 

 Large spots or blotches, especially when surrounded by a 

 light ring, are likewise good reasons for supposing that the 

 individual has not attained its full size. In some forms 

 longitudinal bands become modified, two narrow ones 

 taking the place of a single wide one, or they may be 

 broken up into blotches. Some fish, which are of a simple 

 silvery colour in one place, are spotted in another, and 

 others which have no marks on their bodies throughout 

 their lives frequently have the colour of their fins varying 

 with age. 



There appear to be at least two modes in which variations 

 in colour occur the first due to the interference of light 

 produced by the presence of thin plates ; and secondly, 

 those due to anatomical elements frequently highly 



