Passing to larger organisms--individual and social--we meet the first advance on this arrangement. Where, as among the compound _Hydrozoa_, there is a union of many such primitive groups as form _Hydræ_; or where, as in a _Medusa_, one of these groups has become of great size; there exist rude channels running throughout the substance of the body: not, however, channels for the conveyance of prepared nutriment, but mere prolongations of the digestive cavity, through which the crude chyle-aqueous fluid reaches the remoter parts, and is moved backwards and forwards by the creature's contractions. Do we not find in some of the more advanced primitive communities an analogous condition? When the men, partially or fully united into one society, become numerous--when, as usually happens, they cover a surface of country not everywhere alike in its products--when, more especially, there arise considerable classes which are not industrial; some process of exchange and distribution inevitably arises. Traversing here and there the earth's surface, covered by that vegetation on which human life depends, and in which, as we say, the units of a society are imbedded, there are formed indefinite paths, along which some of the necessaries of life occasionally pass, to be bartered for others which presently come back along the same channels. Note, however, that at first little else but crude commodities are thus transferred--fruits, fish, pigs or cattle, skins, etc.: there are few, if any, manufactured products or articles prepared for consumption. And note also, that such distribution of these unprepared necessaries of life as takes place, is but occasional--goes on with a certain slow, irregular rhythm.