30 THE THEORY OF EVOLUTION 



systematic categories. It is often observed that sack 

 groups in the following series of strata ' suddenly ' 

 extend themselves and thereby split up into numerous 

 families, genera, and species. As a set-off other forms 

 often contemporaneously die out. 



2. Inter-relation between the greater systematic groups 

 (families, classes, and partly orders}. 



If therefore we concede that, on the whole, the 

 higher forms chronologically follow the lower, do they 

 originate therefrom ? 



(1) The Invertebrates appear together in the 

 Cambrian formation, but clearly separated into all 

 the families and most of the classes l which exist 

 at present (see above, page 23). Meanwhile we are 

 absolutely compelled to regard them all as originally 

 separated groups. 



' All the important phylae (families), sharply denned, 

 reach back far into the Cambrian formation, and of 

 those periods in which they might have been united 

 we have no records/ ~ 



We have known for a long time that the majority 

 of the great groups of invertebrate animals are already 

 quite distinctly separated in the Cambrian era. 3 



We cannot therefore deduce as originating from 

 each other the classes of Invertebrates as they have 

 been preserved to the present. 



1 Families, for examples, are the Worms, the Ccelenterata (corals, 

 bryozoa, medusae), in the Sea Urchins (Echinodermata). 



2 E. Koken : Paldontologie und Descendenzlehre, p. 12. 



3 Deperet-Wegner : Die Umbildung der Tierwelt, p. 233. 



