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IV.The Malayan Papilionidæ, or Swallow-tailed Butterflies,

as illustrative of the Theory of Natural Selection.
Special value of the Diurnal Lepidoptera for inquiries of this Nature-

Question of the rank of the Papilionidæ-Distribution of the Papi-
lionidæ-Definition of the word Species-Laws and Modes of Varia-
tion - Simple Variability- Polymorphism or Dimorphism – Local
form or variety-Co-existing Variety-Race or Subspecies--Species
-Variation as specially influenced by Locality-Local Variation of
Size - Local Variation of Form- Local Variations of Colour-Re-

marks on the facts of Local Variation - Mimicry - Concluding

Remarks on Variation in Lepidoptera-Arrangement-Geographical

Distribution - Remarkable peculiarities of the island of Celebes

Concluding Remarks . . . . . . . Pp. 130—-200

V.-On Instinct in Man and Animals.

How Instinct may be best Studied-Definition of Instinct-Does Man
possess Instincts ?—How Indians travel through unknown and track-

orests . . . . . . . . Pp. 201-210

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ON THE LAW WHICH HAS REGULATED THE INTRODUCTION OF NEW SPECIES. *

Geographical Distribution dependent on Geologic

Changes.

the subject of the geographical distribution of animals and plants, must have been interested in the singular facts which it presents. Many of these facts are quite different from what would have been anticipated, and have hitherto been considered as highly curious, but quite inexplicable. None of the explanations attempted from the time of Linnæus are now considered at all satisfactory; none of them have given a cause sufficient to account for the facts known at the time, or comprehensive enough to include all the new facts which have since been, and are daily being added. Of late years, however, a great light has been thrown upon the subject by geological investigations, which have shown that the present state of the earth and of the organisms now

* Written at Sarawak in February, 1855, and published in the “Annals and Magazine of Natural History," September, 1855.

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inhabiting it, is but the last stage of a long and uninterrupted series of changes which it has undergone, and consequently, that to endeavour to explain and account for its present condition without any reference to those changes (as has frequently been done) must lead to very imperfect and erroneous conclusions.

The facts proved by geology are briefly these :That during an immense, but unknown period, the surface of the earth has undergone successive changes; land has sunk beneath the ocean, while fresh land has risen up from it; mountain chains have been elevated ; islands have been formed into continents, and continents submerged till they have become islands; and these changes have taken place, not once merely, but perhaps hundreds, perhaps thousands of times :—That all these operations have been more or less continuous, but unequal in their progress, and during the whole series the organic life of the earth has undergone a corresponding alteration. This alteration also has been gradual, but complete ; after a certain interval not a single species existing which had lived at the commencement of the period. This complete renewal of the forms of life also appears to have occurred several times :—That from the last of the geological epochs to the present or historical epoch, the change of organic life has been gradual : the first appearance of animals now existing can in many cases be traced, their numbers gradually increasing in the more re

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