PKEFACE TO THE FIEST EDITION. 



SEVERAL years ago it was our good fortune to follow, as grad- 

 uate students, a course of lectures and practical study in General 

 Biology under the direction of Professor Martin, at Johns Hop- 

 kins University. So interesting and suggestive was the general 

 method employed in this course which, in its main outlines, had 

 been marked out by Huxley and Martin ten years before, that 

 we were persuaded that beginners in biology should always -be in- 

 troduced to the subject in some similar way. The present work 

 thus owes its origin to the influence of the authors of the 

 " Elementary Biology,' our deep indebtedness to whom we 

 gratefully acknowledge. 



It is still an open question whether the beginner should pur- 

 sue the logical but difncu.lt course of working upwards from the 

 simple to the complex, or adopt the easier and more practical 

 method of working downwards from familiar higher forms. 



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Every teacher of the subject knows how great are the practical 

 difficulties besetting the novice, who, provided for the first time 

 with a compound microscope, is confronted with Yeast, Proto- 

 coccus, or Amoeba ; and on the other hand, how hard it is to sift 



out what is general and essential from the heterogeneous details 

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of a mammal or a flowering plant. In the hope of lessening the 

 practical difficulties of the logical method we venture to submit a 

 course of preliminary study, which we have used for some time 

 with our own classes, and have found practical and effective. 



It has not been our ambition to prepare an exhaustive trea- 

 tise. We have sought only to lead beginners in biology from 



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familiar facts to a better knowledge of how living things are 



built and how they act, such as may rightly take a place in gen- 



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