vi ANIMAL COMMUNITIES 
the particular species and localities covered than upon work done from 
different points of view in remote localities. This bulletin-is not intended 
as a textbook. Several years of work would be necessary to give it the 
completeness and form which a textbook should have, and the physiology 
which should be included in such a textbook is almost entirely omitted. 
The organization here presented has in the main grown out of three 
lines of thought: (a) the physiology of organisms as opposed to the 
physiology of organs (51)'; (6) the phenomena of behavior and physi- 
ology, as illustrated by the studies of Loeb (72), much of the data of 
which can be related to natural environments; and (c) the organized 
comparable data of plant ecology, as set forth by Cowles (58) and 
Warming (12). The results of these five years of labor will not be 
pleasing to many zodlogists because the principles of evolution, heredity, 
etc., have not been correlated. Their omission, however, has not been 
due to any prejudice against their introduction, but rather to the fact 
that they can only occasionally be related to this line of organization. 
It was thought also that the complexity of the problems and concepts 
here treated made separation a nécessity to clearness. 
The number of problems thrown open by the investigation is infinite. 
Naturalistic observation and survey work could be carried much farther 
along the lines here blocked out. The chief lesson which the author has 
drawn from his labors is that experimental study, conducted with due 
reference to the relations of the animals to natural environments, with 
conditions carefully controlled, and a single factor varied at a time, is 
one of the stepping-stones to future progress. We are confronted with 
centuries of animal and human geography, with only inference or specu- 
lation as to controlling factors for a background, and the experimental 
study of factors in the case of man and other land animals only at its 
beginnings. Though man is a land inhabitant, all the best work along 
these and many other lines has been done upon aquatic animals. The 
writer’s course in the future will probably be determined by the needs 
of the science, and will be turned from the purely naturalistic method 
of study to a method made up of naturalistic observations and con- 
trolled experiments. 
In undertaking a new line of work, one must have first, inspiration, 
next, method and motive, and finally, in the case of ecological work, the 
assistance of a large number of persons in various departments of 
knowledge. For such assistance I wish to express my indebtedness to 
: Numbers in parentheses, scattered through this work, refer to references in the 
Bibliography at the end (pp. 325-36). 
