Professor Huxley in delivering the anniversary address to the Geological Society for 1870, quotes the following from an address before the same society in 1862: "If we confine ourselves to positively ascertained facts, the total amount of change in the forms of animal and vegetable life since the existence of such forms is recorded, is small. When compared with the lapse of time since the first appearance of these forms, the amount of change is wonderfully small. Moreover, in each great group of the animal and vegetable kingdoms, there are certain forms which I termed Persistent Types, which have remained, with but very little apparent change, from their first appearance to the present time. In answer to the question, 'What then does an impartial survey of the positively ascertained truths of paleontology testify in relation to the common doctrines of progressive modification, which suppose that modification to have taken place by necessary progress from more to less embryonic forms, from more to less generalized types within the limits of the period represented by the fossiliferous rocks?' I reply, It negatives these doctrines; for it either shows us no evidence of such modifications, or demonstrates such modification as has occurred to have been very slight. The significance of persistent types and of the small amount of change which has taken place even in those forms which can be shown to have been modified, becomes greater and greater in my eyes, the longer I occupy myself with the Biology of the past." From the fact that the trilobites, so highly organized, appeared in the "primordial," or "oldest" strata, it would seem that they were specially adapted to make progress. They lived through "Paleozoic" time, which, according to Dana, represents twelve of the sixteen parts of all geological time, beginning with the Primordial; or, calling the whole geological time 48 millions of years, the trilobites lived 36 million of years, or three-fourths of all geological time. From their great persistence in time (accepting, for the sake of argument, the "ages" of speculative geology) it would seem that they had a remarkably good opportunity to make wonderful progress in structure. During that time there were thousands of species, yet they made no progress. We do not know that in all those "millions of years" a single higher form was evolved from any one of the great multitude of species of trilobites. As Darwin says of the goose, so one may say of the trilobite; it "had a singularly inflexible organization." The remarkable thing about this, however, is that previous to the "Primordial," while it was becoming a trilobite, it must have had a singularly flexible organization, otherwise it could not have obtained its complex structure; but when it reached the "Primordial" it became very conservative. Fairhurst says, in the work already quoted: