36 THE STORY OF FISH LIFE. 



"shedding" them and replacing them by new 

 ones. 



The number and arrangement of the scales are 

 important characters in the determination of 

 fishes. In most fishes they are arranged in 

 obliquely transverse series, and as the number of 

 scales, writes Dr G-iinther, in the lateral line, 

 see below, "generally corresponds to the number 

 of transverse series, it is usual to count the 

 scales in that line. To ascertain the number of 

 longitudinal series of scales, the scales are 

 counted in one of the transverse series, generally 

 that running from the commencement of the 

 dorsal fin, or the middle of the back, to the 

 lateral line, and from the lateral line down to 

 the vent or ventral fin, or middle of the 

 abdomen." 



No one who is observant can fail to have 

 noticed a peculiar and often well-defined line 

 extending from the head to the tail of a 

 fish. Sometimes this runs more or less down 

 the middle of the body, sometimes it is curved, 

 sometimes disconnected, the upper portion of 

 the line terminating abruptly, and the lower 

 portion commencing again below it, to terminate 

 as usual on the tail. This is known as the 

 " lateral line." This line is formed by a series 

 of perforations in the scales. AVhen closely 

 examined these are seen to be filled with mucus, 

 and richly supplied with nerves. From this it is 

 generally held that the lateral line is to be regarded 

 as an organ for the reception of mechanical stimuli 

 transmitted through the surrounding water. In 

 the head this sensory organ is represented by 



