608 VICTOR E. SHELFORD 
b. Inter-psychology and inter-physiology (between ecolog- 
ically similar forms). The problems of the inter-psychology 
(Tarde, ’03) and inter-physiology (p. 588) are equally important 
in connection with the relations suggested above. Some aspects 
of inter-psychology are not inter-specific, but concern forms with 
similar habits. In the steppes ecologically similar animals fre- 
quently act as one species. Mr. Roosevelt has said: ‘‘One of 
the most interesting features of African wild life is close association 
and companionship so often seen between totally different species 
of game” (Roosevelt, 09). Mr. Roosevelt shows the zebra and 
hartebeest herding together. 
c. Intermores-psychology and physiology (between ecologic- 
ally dissimilar forms, or antagonistic forms). The relations of 
animals of different size, habits, ete., to one another involves 
the most striking features of behavior. Much of the behavior 
which tends to protect the species from enemies falls under this 
head. This aspect of behavior has its geographic as well as its 
local significance. For example, the problem of the effect of the 
presence or absence of large carnivores on the behavior of other 
animals present in a climatic formation would deal with the 
broader geographic side. 
d. Geographic variation of mores. The phenomenon of geo- 
graphic variation in behavior and physiology probably usually 
belongs to wide ranging species. The best available data are 
probably on the nesting habits of birds (Knowlton ’09). 
2. The more purely physiological problems. Let us illustrate 
by the desert. The dominance of the reptiles in the desert is 
well known, and Dr. A. P. Mathews has called my attention to 
the fact that the excreta of reptiles is uric acid which is a substance 
of low osmotic pressure passing out with the feces in a dry state; 
little water is used in the disposal of the excreta. This, together 
with the thick skins, enables reptiles to meet the conditions of 
the desert. Desert mammals must meet the same conditions. 
In these, water is required to wash the urine out of the tubules. 
Mammals are few in the desert; their physiological relations there 
are not well known; Swain (’03) has pointed out the high specific 
