PHYSIOLOGICAL ANIMAL GEOGRAPHY 611 
of view is very important. While many aspects of these prob- 
lems are not geographic, many others are, and the study of physi- 
ological animal geography bears the same important relations 
to the study of evolution of behavior as did faunistic animal 
geography to evolution of species in the beginning of its study. 
The relations of animal behavior to the evolution of species 
has never been appreciated. It is obvious that the behavior of 
all animals is regulatory and tends on the whole to preserve the 
species and to retain it in the environmental complex to which it 
is adjusted; still only slight changes in the physiological charac- 
ters of an animal will cause it to select a slightly different complex, 
open entirely new avenues of migration and change the distri- 
bution of the group of species to which it belongs. Such a change 
in physiological character would bring a group of species into an 
entirely different relation to all the so-called factors of evolution 
(McDougal,’08; Tower,’07,’10). Students of experimental evolu- 
tion have, in no case that has come to my attention, made any. 
study of the behavior characters of their new races, while the 
morphological features have been pursued with vigor. Is it not 
time that students of evolution began to study the effects of 
behavior on evolution? 
D. THE FUTURE BIOLOGY 
In this paper we have sharply separated evolution and struc- 
ture on the one hand, from physiology and behavior on the other. 
Space, clearness, and the condition of the subjects have forbidden 
that we attempt to unite them here. While it may be expedient 
to continue in this manner until our knowledge of physiology and 
behavior is commensurate with that of the other subjects, the fol- 
lowing of such a course indefinitely, with respect to either mor- 
phological or physiological aspects of biology cannot, if it be general, 
bring about the best development or unification of biological 
science. Indeed, its present lack of unity is traceable to such a 
course followed until recently by zoologists generally. 
If our understanding of the data of physiological cytology be 
correct, we may expect to find so-called structures of some sort 
within or among the cells concerned in function, which stand for 
