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Each organism's environment, for the most part, consists of other organisms.

That the variability of an organism to a certain extent is a constant and certain condition of life we admit, otherwise there would be no distinguishable individuals of a species.

As in all of biology, comparative studies showing differences among species are often helpful for a better understanding of the basic mechanisms; with all its advantages, there is a danger of clinging exclusively to one model organism.

It is clear to all that the animal organism is a highly complex system consisting of an almost infinite series of parts connected both with one another and, as a total complex, with the surrounding world, with which it is in a state of equilibrium.

In the course of evolution, it constantly happens that, independently of each other, two different forms of life take similar, parallel paths in adapting themselves to the same external circumstances.

Organisms by their design are not made to adapt too far.

No phenomenon can be isolated, but has repercussions through every aspect of our lives. We are learning that we are a fundamental part of nature's ecosystems.

Physiology is concerned with all those phenomena of life that present them selves to us in sense perception as bodily processes, and accordingly form part of that total environment which we name the external world.

Each organism, no matter how simple or complex, has around it a sacred bubble of space, a bit of mobile territoriality which only a few other organisms are allowed to penetrate and then only for short periods of time.

There are many ways for organisms to probe the external world. Some smell it, others listen to it, many see it. Each species, therefore, lives in its own unique sensory world of which other species may be partially or totally unaware.