There still remains one other department of philological inquiry to be considered, and its consideration will tend yet further and most forcibly to corroborate all the general conclusions already attained. Hitherto we have been engaged for the most part on what I have already called the palæontology of human thought as revealed, fossil-like, in the linguistic petrifactions of pre-historic man. But the science of comparative philology is not confined in its researches upon early forms of speech to the bygone remnants of a distant age. On the contrary, just like the science of comparative anatomy, it is furnished with still existing materials for study, which are of the nature of living organisms, and which present so many grades of evolution that the lowest members of the series bring us within easy distance of those aboriginal forms which can only be studied in the fossil state. Hitherto I have considered these lowest existing languages only with reference to their forms of predication. Here I desire to consider them with reference to the quality of ideation that they betoken. In the next instalment of my work I shall have to treat of the psychology of savages, and then it will become apparent that there is no very precise relation to be constantly traced between grades of mental evolution in general, and of language-development in particular. Nevertheless there is a general relation: and therefore it is among the lowest savages that we meet with the lowest types of language-structure.[282] In the present connection I shall have to treat of these languages only in so far as they throw light upon the quality of ideation with which they are concerned, or so far as they are related to the general principles with which we have already been occupied. And, even as thus limited, I will endeavour to make my exposition as brief as possible. I will begin by supplying a few quotations from the more competent authorities who have written upon the subject from a linguistic point of view.