Animals Before Man 



One of the extraordinary things about this 

 early life is the apparent suddenness with 

 which it sprang into being, for it embraces rep- 

 resentatives of no less than seven of the great 

 divisions * of animal life. Neither are these 

 creatures so simple in structure as we might 

 expect them to be from their great antiquity. 

 On the contrary, many are highly specialized 

 in structure, and not so very different from 

 their relatives living to-day and separated from 

 their ancestors by an interval of millions of 

 years. Nor do we find that they intergrade, or 

 show evidences of a common ancestry, so that 

 the line of descent of the crustaceans, for ex- 

 ample, can be traced through them to single- 

 celled protozoans, but the groups are marked 

 off from one another as sharply as now. In 

 the Cambrian sea were sponges and corals, sea- 

 lilies of simple forms (Cystids), brachiopods, 

 shells, and crustaceans ; insects are not as yet 

 known from the Cambrian, but their absence 



* Porifera, sponges ; Coelenterata, corals and jellyfishes • Echi- 

 nodermata; Vermes, worms; Brachiopoda; Mollnsca, shells; Ar- 

 thropoda, trilobites, and other crustaceans. 



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