[46] "Instead of endogamy we might, after some explanations, have used the word caste. But caste connotes several ideas besides that on which we desire to fix attention. On _the other hand, the rule which declares_ the union of persons of the same blood _to be incest_ has been _hitherto unnamed_" (p. 49), and he terms it _exogamy_; and (p. 130) he says, "in all the modern instances in which the symbol of capture is most marked we have found that _marriage within the tribe_ is prohibited as _incest_." [47] Mr M'Lennan (p. 148) says, "We shall endeavour to establish the following propositions:--1. That the _most ancient_ system in which the idea of blood relationship was embodied, was the system of _kinship through females only_. 2. That the primitive groups were, or were assumed to be homogeneous. 3. That the system of kinship _through females only, tended to render_ the _exogamous_ groups _heterogeneous_, and _thus to supersede_ the system of capturing wives." That some tribes should have arrived at some such state through a perverted traditional notion of incest, would, on the other hand, perfectly fit into the theory of degeneracy. I had intended to have pursued this subject, but the chapter has already run to too great length. As allusion however, has been made to Sir John Lubbock, I append an extract (see p. 47) from which it will be seen that his view, although equally remote from historical truth, has a greater _à priori_ probability. Indeed, if we could only consent to start on the assumption of "an initial state of hetairism," nothing would be more complete than the following theory:--