CHAPTER Vn 

 THE AMPHIBIA 



It was very well for the lungfish to lie dormant for 

 months or years in its mud nest, but it was better, and a 

 new way of life, to keep awake by crawling from one 

 water hole to another; and the evolution of the four- 

 footed animals, or tetrapods, which first emerged from 

 aquatic to semi-terrestrial life, is one of the most notable 

 landmarks in vertebrate history. A few invertebrates, such 

 as the scorpions, millepedes, spiders, and perhaps a few 

 wingless insects, had estabHshed themselves on land in 

 the Devonian, but these were small and feeble animals; 

 they subsequently evolved in large variety and numbers, 

 but they failed to achieve the great destiny of the ter- 

 restrial vertebrates. 



The evolution of the Amphibia began in the Devo- 

 nian, the aridity of which had fostered aerial respira- 

 tion in the continental fishes, but it might have come to 

 nought had it not been for the more favorable circum- 

 stances of the Carboniferous. This geologic period de- 

 rives its name from the widespread deposits of coal that 

 were then formed, and was so named in England where, 

 in the coal-bearing seams (or *Coal Measures,* as the 

 English called them), the first half of the period is 

 meagerly preserved. As represented in the United States, 

 however, the 'Carboniferous' is divisible into two dis- 

 tinct and quite dissimilar periods, the Mississippian and 

 the Pennsylvanian. 



