QM 



3 1-7 



USLO. 



PEEP ACE TO THE FOURTH EDITION. 



IN preparing the present edition little change has been 

 made; such errors as have been brought to notice have 

 been corrected, and some changes have been made in the 

 interest of greater clearness or more precise directions. 



The ideal underlying the manual is, as it always has been, 

 to stimulate inquiry and develop the scientific habit of 

 work and thought. The order of presentation remains 

 unchanged, for both from practical and pedagogical reasons 

 such an arrangement has justified itself through years of 

 experience. The order of presentation of topics is, however, 

 of secondary importance, and the individual teacher will 

 make such choice of topics and order of study as best 

 meets his needs. 



An elementary course in biology must of necessity be 

 limited to relatively few typical organisms, but the aim of 

 the manual is distinctly not the study of types as such. 

 In our own course the laboratory study is planned to illus- 

 trate general biological principles such as the following: 

 fundamental plans of animal structure; homology; adap- 

 tation; protoplasmic structure and behavior; development 

 of organisms; and other similar principles. In conducting 

 such a course it is necessary to make definite plans ahead 

 of time, and select from the manual those topics which cover 

 the desired ground. It is believed that there is sufficient 

 material included to make possible a considerable choice to 

 meet varied needs and desires. 



