CHAPTER VII. 

 THE HIGHER ORGANISMS. 



A superficial acquaintance with the structure of 

 familiar living things is sufficient to enable a casual 

 observer to arrrange them in a series in which they pass 

 from the simple unicellular to more and more complex 

 multicellular forms. This does not necessarily mean 

 that it is possible to follow the individual steps through 

 which the complexity was attained, nor does it imply 

 ability to interpret the purpose of the many diverse 

 forms to which this complexity has arrived. Such 

 problems are reserved, for consideration in a future 

 chapter where it is hoped that they may be presented in 

 a reasonable form. 



It is difficult to avoid the conviction that complexity 

 of structure, with the many differentiations and adap- 

 tations it embraces, is of great importance to living 

 substance in improving the conditions of life and better 

 adapting it to the exigencies of existence, yet simply 

 and complexly organized forms of life exist in nature side 

 by side, both equally able to persist. The idea of pur- 

 pose in progress is, therefore, compelled to give place to 

 the opinion that what is seen in this evolution is but 

 evidence of the fact that life is cyclical and subject to 

 changes by which modification is inevitable. The 

 inutility of complexity is further exemplified by the 

 fact that many highly complex and differentiated or- 

 ganisms have become extinct, while many simple organ- 

 isms have persisted. 



With increasing complexity of structure come more 

 complicated conditions of life which make it more and 



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