THE ADVANCE OF ZOOLOGY IN THE NINETEENTH 



CENTURY.* 



George Lefevre. 



The task of reviewing in the limits of a single lecture the 

 progress in the nineteenth century of zoology, a science which 

 has undergone by far the greater and most important part of 

 its development within the century and which to-day presents 

 a vast array of fact and theory, is one of embarrassment of 

 riches. I can only attempt to bring to your attention a few 

 of the more conspicuous achievements of the century in the 

 field of zoology ; to speak briefly of the dawn of the science ; 

 and to indicate the trend of its progress at the present time. 

 In so doing I shall trace the advance along four great lines 

 of zoological development, which, although they often meet 

 and become confluent, receiving from and giving impetus and 

 material to each other, have, nevertheless, advanced more or 

 less independently. It is thus possible to follow the thread 

 continuously through each. These four lines are as follows: 



1. Morphology, or the study of form and structure, includ- 

 ing systematic zoology. 



2. Evolution, or the application of evolutionary principles 

 to organic nature. 



3. The Cell Doctrine, or the doctrine that living things are 

 made up of elementary vital units, termed cells. 



4. Experimental Morphology, or the investigation of the 

 causes underlying the forms and activities of living things, 

 the study of which has been pursued through the experi- 

 mental method. This last line belongs to a very recent date, 

 its main development having taken place within the past 

 decade. 



V . 

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* An address delivered before The Academy of Science of St. Louis, 

 May 20, 1901. 



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