6o EVOLUTION IN THE PAST 



earlier forms have come down to us less their limbs, but 

 from footprints left in the strata it is clear that the Umbs 

 of some of them terminated with what may be called fingers 

 and toes. Most of the later Carboniferous amphibians 

 certainly possessed well-developed digits. The breathing 

 difficulty had, no doubt, been overcome more or less in the 

 same manner as with the lung-fishes. The animals in their 

 youth, it may well be supposed, breathed through gills, for 

 even in present-day amphibians lung-breathing is seldom 

 developed until the adult state is reached. 



The Carboniferous strata, therefore, are not only remark- 

 able for their coal supplies, but also for the evidence they 

 yield of a well-developed and varied hfe of higher rank than 

 fishes. 



