cit., page 16); it occurs in the "Physical History of Mankind," Ed.

2, Volume II., page 570:-- "Is it not probable that the varieties which spring up within the limits of particular species are further adaptations of structure to the circumstances under which the tribe is destined to exist?
Varieties branch out from the common form of a species, just as the forms of species deviate from the common type of a genus.

Why should the one class of phenomena be without end or utility, a mere effect of contingency or chance, more than the other ?" If this passage, and others similar to it, stood alone, we might agree with Prof.Poulton; but this is impossible when we find in Volume I.
of the same edition, page 90, the following uncompromising statement of immutability:-- "The meaning attached to the term species, in natural history, is very simple and obvious.

It includes only one circumstance--namely, an original distinctness and constant transmission of any character.

A race of animals, or plants, marked by any peculiarities of structure which have always been constant and undeviating, constitutes a species." On page 91, in speaking of the idea that the species which make up a genus may have descended from a common form, he says:-- "There must, indeed, be some principle on which the phenomena of resemblance, as well as those of diversity, may be explained; and the reference of several forms to a common type seems calculated to suggest the idea of some original affinity; but, as this is merely a conjecture, it must be kept out of sight when our inquiries respect matters of fact only." This view is again given in Volume II., page 569, where he asks whether we should believe that "at the first production of a genus, when it first grew into existence, some slight modification in the productive causes stamped it originally with all these specific diversities?
Or is it most probable that the modification was subsequent to its origin, and that the genus at its first creation was one and uniform, and afterwards became diversified by the influence of external agents ?" He concludes that "the former of these suppositions is the conclusion to which we are led by all that can be ascertained respecting the limits of species, and the extent of variation under the influence of causes at present existing and operating." In spite of the fact that Prichard did not carry his ideas to their logical conclusion, it may perhaps excite surprise that Mr.Darwin should have spoken of him as absolutely on the side of immutability.
We believe it to be partly accounted for (as Poulton suggests) by the fact that Mr.Darwin possessed only the third edition (1836 and 1837) and the fourth edition (1841-51).