41 6 Life and Immortality. 



gigantic than those of their nearest living relatives. More- 

 over, these ancient forms of life represent what are called 

 comprehensive types, or types that possess characters in 

 combination such as are nowadays found separately devel- 

 oped in different groups of animals. Such permanent reten- 

 tion of embryonic characters and comprehensiveness of 

 structural type are signs of what zoologists consider to be 

 comparatively low grades of organization, and their preva- 

 lence in the earlier forms of animals is a very astonishing 

 phenomenon, though they are none the less perfectly organ- 

 ized so far as their peculiar type is concerned. As we ascend 

 the geological scale, these features will be found to gradu- 

 ally disappear, higher and even higher forms will be intro- 

 duced, and specialization of type take the place of the former 

 comprehensiveness. That there has been in the past a gen- 

 eral progression of organic types, and that the appearance of 

 the lower forms of life has in the main preceded that of the 

 higher forms in point of time, is a widely-accepted generaliza- 

 tion of palaeontology. 



Now that it has been seen that there has been a gradual 

 progression and development of animal types all through 

 the ages up to the era of man, the question naturally occurs 

 whether or not the changes are still going on which will 

 result in a higher development. Man coexisted in Western 

 Europe with several remarkable mammals in the later por- 

 tion of the Post-Pliocene Period. While we do not know 

 the causes which led to the extinction of the mammoth, 

 woolly rhinoceros, cave-lion and others, yet we do know that 

 scarcely any mammalian species have become extinct during 

 the historical period. The species with which man coexisted 

 are such that presumably required a very different climate to 

 that now prevailing in Western Europe. Some of the depos- 

 its in which man's remains have been found in association 

 with the bones of extinct mammals incontestably show that 

 great changes in the physiography and surface-configuration 

 of the country had taken place since the period of their 



