30 THE STORY OF FISH LIFE. 



modified — probably by fusion of many to form 

 one — so as to form a complete coat of armour. 

 These fused scales take the form of broad bars, 

 or perhaps they had better be called shields. 

 They are arranged in a double series, an upper 

 or back shield, which extends downwards to the 

 middle of the body; and a lower shield, which 

 clothes the lower part of the body or abdomen, 

 the lower shield commencing at the point where 

 the back shield terminates. There are a great 

 number of these shields following one behind the 

 other, from the head backwards. They are what 

 is called metamerically arranged. That is to say, 

 if the body were cut into a number of pieces 

 corresponding to the number of the bones in the 

 vertebral column, there would be one pair of 

 shields — a dorsal and ventral — to every vertebra. 

 This metameric arrangement is a point of deep 

 significance. 



In the coffer -fish (Ostracion) of the West 

 Indies, the scales have been modified into a 

 series of hexagonal plates, fitting closely together 

 like mosaic work. As a result, the fish is en- 

 closed in a kind of box, hence its name coffer- 

 fish. From this box only the fins and tail 

 project, or are capable of movement. 



In a species of Diodon (Chilomi/derus reticulatus), 

 of tropical seas, the scales are small, very dense, 

 and have broad tri-radiate bony roots, so that 

 the scales are widely separated one from another, 

 touching only at three points representing the 

 tip of each root. In another species of this same 

 genus (Diodon), called the porcupine fish, the 

 scale grows to a greater length, forming a bony 



