REPTILES AND AMPHIBIANS 121 



the pterodactyl. It was not itself very large, but it had 

 relatives with wings that measured eight yards. 



We have to go further baek in the history of the 

 earth for the period when the amphibians flourished 

 most. The largest forms of this class lived in the 

 Permian and Triassic periods. These were the 

 stegocephala, huge beasts that lay in ambush for their 

 victims in the prickly thickets. The yard-long jaws of 

 the mastodonsauri were armed with numbers of sharp 

 teeth ; their belly and skull were protected by powerful 

 armour, and they had, besides the two eyes, a third or 

 Cyclopean eye in the middle of the forehead. 



The fact that the amphibians were before the reptiles 

 in the history of the earth is a proof that the latter 

 descended from the former. Geology shows that the 

 succession of the five classes of vertebrates was the 

 same in the history of the animal world as it is in our 

 classification. The earliest geological finds known to 

 us are remains of fishes alone, and these increase in 

 variety. The first amphibians appear in the Car- 

 boniferous period, and they are followed in later epochs 

 by the reptiles. In the Jurassic strata we find the first 

 bird, the archeopteryx, of which we spoke above ; and 

 the mammals do not reach the height of their 

 development until the Tertiary period. 



But, it will be said, fishes are highly organised animals, 



and according to our theory there can only have been 



extremely simple organisms in the beginning. How 



is it, then, that we find fishes in the oldest strata .■* ^ 



1 To be quite accurate, in the second oldest, the Silurian. But as 

 these fishes have an advanced organisation, it is clear that there must 

 have been fishes in the oldest period known to us, the Cambrian. 



