238 SCALES OF FISHES. 



kerel may be quoted as one of the most elegant in 

 shape, as well as perfect in its adaptation, to the ele- 

 ment in which it moves, but the external figures of 

 several species have been accurately measured and 

 studied by naval architects for models of vessels, as 

 speed or tonnage might be the power required. 



The surface of the body is, in most instances, 

 covered by scales, which vary considerably in size, num- 

 ber, and thickness, according to the species. Each 

 scale is attached to the skin of the fish by its anterior 

 edge, and in arrangement they overlap each other. 

 They exhibit in their structure both radiating and 

 concentric lines, or strise. If examined with a lens of 

 sufficient magnifying power, the 

 straight or radiating lines indicate 

 the situation of minute tubes con- 



;' \''\ 



veying a fluid, by which the sub- 

 ^iKJfi stance of the scale is nourished. 

 The concentric lines mark the 

 edges of the laminae forming the 



SCALE OP ORET MULLET. 



scale itself, the outermost line 

 being the edge or margin of the last layer deposited on 

 its inner surface, and the number of these lines be- 

 comes greater as the fish advances in age, thus mark- 

 ing the growth. The row of scales along the side of 

 the fish, forming the lateral line, in addition to the 

 structure common to the scales on the other parts of 

 the body, are pierced in their centre by a tube which 

 allows the escape of the mucous secretion produced 

 by the glands underneath them. The scales may be 

 considered as defending the skin of the fish from the 



