6 ANIMAL LIFE PAST AND PRESENT. 



or whether it was always of the same type as at 

 present, is one of those questions which does not yet 

 admit of a decisive answer. In contrast to the Ganoid 

 fishes, where we see a gradual dying out of the old 

 mail-clad types, we may notice the case of the Sharks 

 and Eays. These fishes seem to have taken a moderate 

 course in regard to armour, avoiding on the one hand 

 the plate-armour of the Ganoids, and on the other the 

 light scale-armour of the fishes of the present day. In 

 most of these fishes the skin is studded with very 

 small bony granules, and thus has a rough file-like 

 structure, being commonly known under the name of 

 shagreen. These fishes, be it noted, while among the 

 earliest known forms, are still extremely abundant, 

 and thus present a striking instance of the advantage 

 of a middle course in the struggle for existence. 



By far the great majority of the fishes of the present 

 day belong, however, to a group which seems to have 

 made its appearance shortly before our Chalk was 

 deposited, and is now the dominant one. These 

 modern fishes have succeeded in entirely getting rid 

 of the plate-armour of the Ganoids, for which they 

 have substituted a much lighter scale-armour formed 

 of the well-known overlapping horny scales which 

 give the silvery lustre we admire so much in the 

 roach and salmon. The same type of armour also 

 obtains in the curious Baramunda of Queensland 

 (Fig. 3), which belongs to an older group. Whereas, 

 however, the majority of the fishes of the present day 

 have adopted this light scale-armour in place of the 



