7o THE DARWINIAN THEORY 



no one primary division of the animal kingdom is 

 entirely extinct : it is merely the subdivisions that 

 have died out. The earliest origin of all the great 

 groups is driven back to extremely remote times, to 

 the Palaeozoic period, and palaeontology tells us 

 nothing about the mode of origin of the great 

 divisions of animals. Darwin says : " I look at the 

 geological record as a history of the world imperfectly 

 kept, and written in a changing dialect ; of this 

 history we possess the last volume alone, relating 

 only to two or three countries. Of this volume, only 

 here and there a short chapter has been preserved ; 

 and of each page, only here and there a few lines. 

 Each word of the slowly changing language, more or 

 less different in the successive chapters, may represent 

 the forms of life which are entombed in one con- 

 secutive formation, and which falsely appear to us to 

 have been abruptly introduced. On this view the 

 difficulties above discussed are greatly diminished, 

 or even disappear." 



Geographical Distribution. 



The explanation of the distribution of animals on 

 land and in the sea is a subject of great importance, 

 which I propose here to touch upon only as it is 

 affected by palaeontological evidence. 



Much information has been collected on this 

 subject by exploration and by systematic obser- 

 vations obtained by dredging expeditions. A 

 gradually growing conviction has arisen that we 

 must not be content with mere facts, but must 



