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* The fundamental and most difficult question remaining in natural history is here presented the question whether this actual geographical association of congeneric or other nearly related species is primordial and therefore beyond all scientific explanation or whether even this may be to a certain extent a natural result. The only noteworthy attempt at a scientific solution of the problem aiming to bring the variety as well as the geographical association of existing species more within the domain of cause and effect is that of Mr. Darwin and later of Mr. Wallace partially sketched in their short papers. On the Tendency of Species to form varieties and on the Perpetuation of Varieties and Species by natural Means of Selection in the Journal of the Proceedings of the Linnæan Society vol. iii Zoology p. 45. The views there suggested must bear a prominent part in future investigations into the distribution and probable origin of species. It will hardly be doubted that the tendencies and causes indicated are really operative the question is as to the extent of their operation. But I am already disposed on these and other grounds to admit that what are termed closely related species may in many cases be lineal descend-

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ants from a pristine stock just as domesticated races are or in other words that the limits of occasional variation in species if by them we mean primordial forms are wider than is generally supposed and that derivative forms when segregated may be as constantly reproduced as their originals.

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