PREFACE 



THE present work is not a book on Protozoology, but on 

 Genetics, employing Protozoa as material, and compar- 

 ing the conditions there found with those in higher organ- 

 isms. 



To select from a great mass of varied material, not yet 

 reduced by science to unity, those features that appear 

 most significant for certain general questions is a task of 

 difficulty, not unattended with the danger of justifying 

 the critic. I cannot hope to entirely escape that danger. 

 Much that is of extreme interest must be omitted, if any 

 clearness of outline is to be preserved. A certain one- 

 sidedness appears inevitable, unless an encyclopedic work 

 is attempted. The relatively great prominence given to 

 the infusoria in these lectures is an example; the hetero- 

 geneous and still more imperfectly known genetic phe- 

 nomena in the other Protozoa lend themselves less readily to 

 a unified presentation. I can only hope that the limita- 

 tions of the work aid in defining certain large problems. 



Technical terms have been avoided. This is not alone 

 because the lectures were for an audience not composed 

 of specialists. Technical terms, in spite of their con- 

 venience, bring many disadvantages, even in strict scientific 

 work. They seem to give to phenomena a distinctness and 

 uniqueness which does not exist in nature. They create 

 separate entities for things that are mere variations on a 

 general theme. Any phenomenon has many-sided relations 

 to the others ; to bring these out we have not hesitated even 

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