x ANIMAL COMMUNITIES 
work is based, that the survey aspect of ecology is a subject for co- 
operative investigation. Because of the complexity of the problems, it 
has been deemed advisable to publish this work even in its present 
preliminary and necessarily incomplete form, in order to make the 
material accessible as soon as possible to teachers, investigators, and 
others who are interested. 
DEPARTMENT OF ZOOLOGY 
UNIVERSITY OF CHICAGO 
September 9, 1912 
