APPARITION OF SPECIES 97 



time without any perceptible advance in rank or com 

 plexity of structure. If, then, we admit the animal 

 nature of this earliest fossil, we can derive from it 

 no evidence of spontaneous evolution ; and if we 

 deny its animal nature, we are confronted with a 

 still graver difficulty in the next succeeding forma 

 tions. 



Between the rocks which contain Eozoon and the 

 next in which we find any abundant remains of life 

 there is a gap in geological history either destitute of 

 evidence of life or showing nothing materially in 

 advance of Eozoon. In the Cambrian age, however, 

 we obtain a vast and varied accession of living things, 

 which appear at once, as if by a sudden and simul 

 taneous production of many kinds of animals. Here 

 we find evidence that the sea swarmed with living 

 creatures near akin to those which still inhabit it, and 

 nearly as varied. Referring merely to leading groups, 

 we have many species of the soft shellfishes, or crus 

 taceans, and the worms, the ordinary shellfishes, the 

 sea-stars, and the sponges. 1 In short, had we been 

 able to drop our dredge into the Cambrian or Silurian 

 ocean, we should have brought up representatives of 

 all the leading types of invertebrate life that exist in 

 the modern seas different, it is true, in details of 

 structure from those now existing, but constructed on 



1 From the lowest Cambrian beds in which definite and abundant 

 forms of life are first met with we have all the leading types of marine 

 invertebrate life, represented by at least 165 species and 67 genera, 

 according to Walcott. 



G 



