612 VICTOR E SHELFORD 
or are correlated with each physiological state and physiological 
condition to which we have referred. Our methods may not. at 
present be sufficiently delicate to detect such structure, or the 
processes which lie back of it, but we may, it is believed, confi- 
dently expect the necessary methods for the detection of such 
structures and processes, and especially their correlation with 
and relation to the more permanent and more easily recogniz- 
able morphological conditions. 
We classify the responses and changes in animals as evolution, 
modification by the environment, behavior and physiological 
response. Are not all these, after all, but different expressions 
of the same or similar processes? Future investigations must 
answer this question and it is around this question that the future 
of much that is known as biology hinges. 
V. GENERAL CONCLUSIONS AND SUMMARY 
1. Distribution and dispersal 
a. Every animal selects an environmental complex as its 
general habitat (pp. 566, 571, 579). 
b. The breeding grounds are usually the most important index 
of the true habitat (p. 587). 
c. Each species is usually distributed as far as its environ- 
mental complex e>tends, unless barriers are encountered; faun- 
istic animal geography begins where physiological animal geo- 
graphy leaves off (pp. 573, 582, 598). 
d. Thesuccess of a species within a territory and its limitations 
to that territory are determined by fluctuation of one or more 
environmental factors, toward or beyond the limit tolerated by 
the species (p. 599). 
e. Species which select those environmental complexes which 
are determined by streams, soil, or other situations which occur 
only locally, are local in their distribution (pp. 574, 5). 
f. Animals which select a habitat which is geographic in extent 
and which represents the dominant conditions of an area, are 
distributed throughout their area and are usually not so wide 
ranging as the species which select the local conditions (p. 582). 
