ZOOGENESIS 



tiality was present for the occurrence of some repre- 

 sentative type or types in each of the phyla or major 

 groups without at the same time denying the validity 

 of our interpretations of the processes of geology so 

 far as concerns the disintegration of the rocks and the 

 building up of soils and sediments. And such fossil 

 evidence as exists, fragmentary and unsatisfactory as 

 it is, supports the assumption that this potentiality 

 was an actuality and that animal life so far as the 

 phyla are concerned at the very first appeared in essen- 

 tially the same form as that in which we know it now. 



While at the time of the first appearance of life the 

 abundant water and the winds and the disintegration 

 of the rocks rendered possible the existence of animals 

 in all the major groups, conditions on the earth were 

 very different from those at the present day. 



We learn this from the constantly varying assem- 

 blages of fossils in the rocks of different ages. Thus 

 in the Cambrian rocks we find occurring together 

 animal types which now are exclusively marine, as 

 the sea-cucumbers, brachiopods (fig. 60, p. iii), 

 gephyreans and others, some of which live in shallow 

 water and others only in the deep sea; types, such 

 as the phyllopods which now are exclusively non- 

 marine, living in rivers, lakes and ponds; and types, 

 as the nereid worms (fig. 85, p. 161), with modern 

 representatives both in the sea and in fresh water. 



All of the creatures which we know from the Cam- 

 brian, with the possible exception of the trilobites, 

 were very delicate and fragile. This suggests that 

 at that time the water where they lived was quiet. 



