4 THE SNAKES OF SOUTH AFRICA. 



find more highly-evolved creatures, such as fish without bony 

 backbones, or backbones composed of cartilaginous matter. 

 These are known as the Silurian fishes, of which our present-day 

 Shark Family is an example. 



As we slowly ascend we find the fishes gradually becoming 

 more highly developed or specialized ; and when we reach what 

 is known as the Devonian System, or, in other words, the time 

 in the earth's history many milhons of years ago when the old 



Fig. I. — These are Flying Reptiles or Winged Dragons. They lived millions of years ago. 

 Their fossil remains have been found preserved in the oolitic rocks. Some of them measured 

 i8 feet across the expanded wings. These Winged Dragons and the reptile ancestors of 

 birds doubtless sprang from the same common stock, viz. some form of Flying Reptile. 

 (From " Extinct Animals " by Sir Ray Lankester.) 



Red Sandstone was deposited as sediment and formed into hard 

 rock, we discover the higher order of scaled fishes with real true 

 backbones of hard bony matter. These were the first to evolve 

 real bony skeletons, i.e. forms of life with true backbones. 

 Their ancestors had soft skeletons, but were slowly evolving 

 a bony structure. We find, too, in the Silurian period 

 already referred to that the creatures we call Silurian fish 

 abounded, and that these fish were the hnk between the true 



