the transformed food substances, which are then passed on to the other parts of the body.  It is hardly necessary to point out that the ingestive structures for taking food and preparing it mechanically lie at and near the mouth, while the digesting parts, like the stomach, come next, because chemical transformation is the next thing to be done; while finally the absorbing portions of the tract, or the intestines, come last.  The second group of organs, like gills and lungs, supplies the oxygen, which is as necessary for life as food itself; this respiratory system also provides for the passage from the body of certain of the waste gases, like carbonic acid gas and water vapor.  The excretory system of kidneys and similar structures collects the ash-waste produced by the burning tissues, and discharges this from the whole mechanism, like the ash hoist of a steamship.  The circulatory system, made up of smaller and larger vessels, with or without a heart, transports and propels the blood through the body, carrying the absorbed foods, the supplies of oxygen, and the waste substances of various kinds.  All of these four systems are concerned with “commissary” problems, so to speak, which every individual must solve for and by itself.

Another group of systems is concerned with wider relations of the individual and its activities.  For example, the motor system accomplishes the movements of the various organs within the body, and it also enables the organism to move about; thus it provides for motion and locomotion.  Systems of support, comprising bones or shells, occur in many animals where the other organs are soft or weak.  Perhaps the most interesting of the individual systems of relation is the nervous system.  The strands of its nerve fibers and its groups of cells keep the various organs of the body properly cooerdinated, whereas in the second place, through the sensitive structures at the surface of the body, they receive the impressions from the outside world and so enable the organism to relate itself properly to its environment.  The last organic system differs from the other seven in that the performance of its task is of far less importance to the individual than it is to the race as a whole.  It is the reproductive system, with a function that must be always biologically supreme.  We can very readily see why this must be so; it is because nature has no place for a species which permits the performance of any individual function to gain ascendency over the necessary task of perpetuating the kind.  Nature does not tolerate race suicide.

All organisms must perform these eight functions in one way or another.  The bacterium, the simplest animal, the lowest plant, the higher plants and animals,—­all of these have a biological problem to solve which comprises eight terms or parts, no more and no less.  This is surely an astonishing agreement when we consider the varied forms of living creatures.  And perhaps when we see that this is true we may understand why adaptation is a characteristic of all organisms, for they all have similar biological problems to solve, and their lives must necessarily be adjusted in somewhat similar ways to their surroundings.