176 WALKS AND TALKS. 



back-bones, skulls, limbs, and teeth. It is doubtful whether 

 they belonged to vertebrates as high even as reptiles. You 

 remember that the beds of ancient reptiles were passed at 

 higher levels. The bones here seem to be those of Amphib- 

 ians and Fishes. Amphibians, perhaps you understand, are 

 reptile-shaped animals which breathe water when young and 

 air when adult. Frogs and toads are living Amphibians with- 

 out tail. Salamanders, tritons, axolotls, and fish-lizards are 

 Amphibians with tails. But fish-lizards retain their gills 

 throughout life. The gills are beautifully fringed, scarlet, ex- 

 ternal appendages, projecting from the neck on each side. 

 We call them amphibians because in their structure they so 

 much resemble salamanders. Moreover, the axolotl, while in 

 the elevated regions of Colorado it retains its gills permanently, 

 in less elevated regions, absorbs them and becomes a sala- 

 mander. So it happens that the permanence or absorption of 

 the gills is not a circumstance of very great importance. 



This thought leads me to add that in the plan of all ver- 

 tebrates, provision is made for the development of both gills 

 and lungs ; but generally only one sort of respiratory organ 

 is actually developed ; and that depends on the life the animal 

 is to lead. Man himself has provision for gills in the early 

 embryonic stages of his being. The eggs of Amphibians are 

 deposited and hatched in water, and the young must, there- 

 fore, be fitted with gills. All vertebrates below Amphibians 

 have gills for a permanency ; all above, have lungs for a per- 

 manency. The Amphibian is on the dividing line. In the 

 lowest phase of its existence, it goes with fishes ; in the highest 

 phase, it goes with reptiles. Its life is double. But, on the 

 one hand, the separating line leaves the fish-lizard wholly on 

 the aquatic side ; and so, on the other it leaves the toad, in 

 some cases, wholly on the land side ; since toads sometimes 

 rear their young without finding their way to the water. 



These amphibious border-land creatures possess very great 

 interest ; and so this type of creatures fossilized in the Coal 

 Measures, throws much light on the problem of life and 

 organization. They are border-land creatures here in an addi- 



