ANIMAL LIFE AND THE MICROSCOPE 



particles of lime which may be seen under a higher 

 magnification. 



Perch, pike, sole and some other fish have much 

 more peculiar scales, known as ctenoid or combed 

 for the reason that their unattached, that is to say 

 their hinder margins, are toothed like a comb. 



The scales of sharks, dog-fish and rays are called 

 placoid for they are toothed; not only so but their 

 arrangement is frequently quite dissimilar to the 

 scales of ordinary fish. Taking the herring as our 

 example, but a salmon or any other fish would serve 

 equally well, and examining the arrangement of its 

 scales with the help of our pocket lens, we shall 

 find that the scales are fixed to the fish by their 

 forward edges and that each scale partly overlaps 

 its neighbour, as do tiles on a roof. In the shark 

 family, however, the scales are often relatively wide 

 apart, they do not overlap but are imbedded 

 separately in the skin. The scales of rays have each 

 a hard spine projecting from the centre, those of 

 sharks and dog-fish have teeth, and they are teeth 

 not only in appearance but also in structure. 



The ganoid scales of sturgeon we are hardly likely 

 to meet with. Sometimes these fish are on sale in 

 London and other large towns and a specimen of 

 their scales may be procured. They are bony in 

 structure and, though interesting, require a con- 

 siderable amount of preparation to render them 

 sufficiently transparent to be examined under the 

 microscope. 



It is interesting to note that all the fossil fish 

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