PHYSIOLOGICAL ANIMAL GEOGRAPHY 591 
Ill. THE PHYSIOLOGICAL CHARACTERS AND DISTRIBUTION OF 
GROUPS OF SPECIES (FORMATIONS) 
A. ZOOLOGICAL OPINIONS AND DIFFICULTIES 
There is, I believe, a general opinion among laboratory zool- 
ogists to the effect that no important generalizations can be made 
from data concerning the environmental relations of animals. 
In other words, the data of natural history cannot be organized 
into a science. 
There are at least three good reasons for the prevalence of such 
views. ‘The first of these is that such zoologists are often familiar 
with only a few of the very common species of animals, common 
because their habitat relations are such that they can flourish 
in the conditions which civilization produces or because they do 
not have definite habitat relations, being in this respect an excep- 
tion to the rule. The lack of attention to the taxonomy of com- 
mon forms is also a factor. Animals which belong to different 
species, genera, or even families, are often quite similar in appear- 
ance and so are sometimes regarded as single species. Articles 
regarding American species have occasionally been published 
under the names of Kuropean species not found in this country, 
or at least rare and confined to northern latitudes. 
The second reason results from the fact that relations of animals 
to their environment are not understood. Often we do not dis- 
eriminate between the important and unimportant periods of 
relation to environment in a life-history. The third reason lies 
in the fact that the environment of animals is also not understood 
and the various stages and phases have not been classified so that 
habitat relations can be readily described. 
The lack of knowledge of taxonomy and the simpler facts of 
natural history requires no discussion. On the other hand, our 
knowledge of animal behavior and animal physiology has been 
but little applied in the study of animals in nature, and the knowl- 
edge of environments, which is in the hands of the plant ecologists 
and geographers is not at all well known among zoologists. 
