4 ANIMAL LIFE PAST AND PRESENT. 



of larger or smaller shield-like bones closely united 

 together at their edges. The head, too, in some of 

 these fishes (Fig. 1) was most remarkable, and looked 

 something like a flattened and expanded ploughshare. 

 It has, indeed, been suggested that the reason why 

 these earliest fishes possessed such an extraordinary 

 strong coat-of-mail is that the waters of the primeval 

 epochs were hot from contact with the still heated 

 globe, and were also impregnated with strong acids or 

 salts; but against this it may be urged that it does 

 not appear that it would be any advantage to be par- 

 boiled in a coat-of-mail rather than in an ordinary 



FIG. 1.- An Armoured Fish (Cephalaspis) of the Old Red Sandstone. 



skin. Somewhat later in the world's history, that is 

 to say, at and about the period when our coal was 

 formed, fishes with an armour of a different type were 

 very abundant ; many of the same groups also occur- 

 ring in the Old Eed Sandstone. In these Ganoid 

 fishes, as they are scientifically termed, the body 

 (Fig. 2) was often covered with a coat of lozenge- 

 shaped scales, formed of solid bone, and faced with 

 a hard coating of shining and polished enamel. These 

 scales did not, as in most fishes of the present day, 

 overlap one another like the slates on a roof, but were 

 joined together at their edges, frequently with the 



