n PROGRESS OF PALEONTOLOGY 41 



life. He observed that the oldest fishes present 

 many characters which recall thje embryonic con- 

 ditions of existing fishes ; and that, not only among 

 fishes, but in several groups of the invertebrata 

 which have a long palasontological history, the 

 latest forms are more modified, more specialised, 

 than the earlier. The fact that the dentition of 

 the older tertiary ungulate and carnivorous mam- 

 mals is always complete, noticed by Professor 

 Owen, illustrated the same generalisation. 



Another no less suggestive observation was made 

 by Mr. Darwin, whose personal investigations 

 during the voyage of the Beagle led him to remark 

 upon the singular fact, that the fauna, which im- 

 mediately precedes that at present existing in any 

 geographical province of distribution, presents the 

 same peculiarities as its successor. Thus, in 

 South America and in Australia, the later tertiary 

 or quaternary fossils show that the fauna which 

 immediately preceded that of the present day 

 was, in the one case, as much characterised by 

 edentates and, in the other, by marsupials as it is 

 now, although the species of the older are largely 

 different from those of the newer fauna. 



However clearly these indications might point 

 in one direction, the question of the exact relation 

 of the successive forms of animal and vegetable 

 life could be satisfactorily settled only in one way ; 

 namely, by comparing, stage by stage, the series of 

 forms presented by one and the same type through- 



