CHAPTER 4 



FROM SINGLE CELLS TO MANY CELLS 



Once the fully organized cell had evolved 

 on earth, it undoubtedly explored thou- 

 sands of possibilities in structural patterns 

 as well as environments in which to live. 

 Some found niches in which they were 

 "satisfied," where they have remained 

 through the succeeding millions of years. 

 We find them still occupying these same, 

 or very similar, places today. They 

 found no need for change, no need to 

 search elsewhere for more favorable fea- 

 tures in their environment. Others, how- 

 ever, were forced into situations where 

 they were subjected to a variety of en- 

 vironments which compelled them to 

 change or perish. It was from this group 

 that we might expect to find not only new 



varieties of single cells but also some that 

 banded themselves together in small groups 

 for the sake of "better living," whatever 

 that entails. 



The colonial idea proved advantageous 

 for survival, and more and more cells were 

 added until the mass became so great that 

 changes became necessary to permit the 

 continuing of the vital life functions. Sys- 

 tems for surmounting these encroaching im- 

 pairments of function were introduced in 

 a diversity of form and structure; some 

 proved efficient and allowed the animal to 

 become still more complex, others must 

 have been so poor that the organism 

 changed no more or died out. From this 

 long, tortuous path has come to us today 



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