HOW FISH ARE CLOTHED. 31 



rod resembling the quill of a porcupine — hence 

 its name. 



In the sea-horse the scales are cruciform in 

 shape, and interlaced so as to form an outer 

 skeleton, which, when complete, may be com- 

 pared to filagree work. 



In another very remarkable form, the tortoise- 

 fish (Amphisile), of the waters of the Indo-Pacilic, 

 the scales have become completely replaced by a 

 bony cuirass, which is prolonged backwards into 

 a spine beyond the tail. This remarkable cuirass 

 has been shown by Dr Giinther to be formed 

 entirely by the bones of the skeleton, like the 

 carapace of the tortoise. 



But the scales of a fish, like every other part 

 of its body, must have had a beginning, and if 

 we cannot exactly say what was the nature of 

 this beginning, we can, at least, with tolerable 

 certainty, point to the fish which bear to-day the 

 most primitive form of scales. Such fish we find 

 in the sharks and rays. With the sharks, of 

 course, we include also the dog-fish. Here, in 

 fishes of this type, we find the scales of the 

 higher forms represented by dense nodules, 

 varying greatly in size, embedded in the skin. 

 If one of these nodules be examined (fig. 4, B.), 

 two distinct parts will be distinguishable — a 

 bone-like base, embedded in the skin, during life, 

 and a superficial more dense enamel - covered 

 portion, which is generally spine-like. If one of 

 these primitive scales be compared with a tooth 

 from the same fish, we shall be struck with the 

 very close resemblance between the two. On 

 account of this resemblance, these scales are 



