Two beings may then form what is to the eyes a single mass, and may live, not only in contact with each other, but even in a state of mutual penetration without constituting a society. It is enough in such a case that one looks at them as entirely distinct, that their activities tend to opposite or merely different ends. If their functions, instead of co-operating, diverge; if the good of one is the evil of the other, whatever the intimacy of their contact may be, no social bond unites them. But the nature of the functions and the form of the organs are inseparable. If two beings are endowed with functions that necessarily combine, they are also endowed with organs, if not similar, at least corresponding. And these beings with like or corresponding organs are either of the same species or of very nearly the same species. However, circumstances may be met where two beings with quite different organs and belonging even to widely remote species may be accidentally and at a single point useful to each other. A habitual relation may be established between their activities, but only on this one point, and in the time limits in which the usefulness exists. Such a case gives the occasion, if not for a society, at least for an association; that is to say, a union less necessary, less strict, less durable, may find its origin in such a meeting. In other words, beside the normal societies formed of elements specifically alike, which cannot exist without each other, there will be room for more accidental groupings, formed of elements more or less specifically unlike, which convenience unites and not necessity. We will commence with a study of the latter.