386 PALAEONTOLOGY AND EVOLUTION xi 



them; or they formed part of the population of 

 some other distributional province of that day, 

 and only entered our area by migration at the end 

 of the Devonian epoch. Whether Reptilia and 

 Mammalia existed along with them is to me, at 

 present, a perfectly open question, which is just 

 as likely to receive an affirmative as a negative 

 answer from future inquirers. 



Let me now gather together the threads of my 

 argumentation into the form of a connected hypo- 

 thetical view of the manner in which the dis- 

 tribution of living and extinct animals has been 

 brought about. 



I conceive that distinct provinces of the distribu- 

 tion of terrestrial life have existed since the earliest 

 period at which that life is recorded, and possibly 

 much earlier; and I suppose, with Mr. Darwin, 

 that the progress of modification of terrestrial 

 forms is more rapid in areas of elevation than in 

 areas of depression. I take it to be certain that 

 Labyrinthodont Amphibia existed in the distribu- 

 tional province which included the dry land 

 depressed during the Carboniferous epoch ; and 

 I conceive that, in some other distributional 

 provinces of that day, which remained in the 

 condition of stationary or of increasing dry land, 

 the various types of the terrestrial Saurop&ida 

 and of the Mammalia were gradually developing. 



The Permian epoch marks the commencement 

 of a new movement of upheaval in our area, which 

 attained its maximum in the Triassic epoch, when 



