Educ T20298,35.5305,3 AUG 1 3 1921 HARVARD COLLEGE LIBRARY GIFT OF GEORGE ARTHUR PLIMPTON JANUARY 25, 1924 PRINCIPLES OF GEOLOGY. BOOK III. CHAPTER VII. LAWS WHICH REGULATE THE GEOGRAPHICAL DISTRIBU - Geographical distribution and migrations of fish—of testacea — of zoophytes-Distribution of insects — Migratory instincts of some species- Certain types characterize particular countries -Their means of dissemination- Geographical distribution and diffusion of man-Speculations as to the birth-place of the human species-Progress of human population — Drifting of canoes to vast distances - On the involuntary influence of man in extending the range of many other species. Geographical Distribution and Migrations of Fish.ALTHOUGH We are less acquainted with the habitations of marine animals than with the grouping of the terrestrial species before described, yet it is well ascertained that their distribution is governed by the same general laws. The testimony borne by MM. Péron and Lesueur to this important fact is remarkably strong. These eminent naturalists, after collecting and describing many thousand species of marine animals which they brought to Europe from the south ern hemisphere, insist most emphatically on their distinctness from those north of the equator; and this remark they extend to animals of all classes, from those of a more simple to those of a more complex organization—from the sponges and medusæ to the cetacea. Among all those which we have been able to examine," say they, "with our own eyes, or with regard to which it has appeared to us possible to pronounce with certainty, there is not a single animal of the southern regions which is not distinguished by essential characters from the analogous species in the northern seas. * The fish of the Arabian gulf are said to differ entirely from those of the Mediterranean, notwithstanding the proximity of these seas. The flying-fish are found (some stragglers excepted) only between the tropics; in receding from the Line, they never approach a higher latitude than the fortieth parallel. Those inhabiting the Atlantic are said to be different species from those of the eastern ocean.† The electric gymnotus belongs exclusively to America; the trembler, or Silurus electricus, to the rivers of Africa ; but the torpedo, or cramp-fish, is said to be dispersed over all tropical, and many temperate seas. All are aware, that there are certain fish of passage which have their periodical migrations, like some tribes of birds. The salmon, towards the season of spawning, ascends the rivers for hundreds of miles, leaping up the cataracts which it meets in its course, and then retreats again into the depths of the ocean. The *Sur les Habitations des Animaux Marins.-Ann. du Mus., tom. xv., cited by Prichard, Phys. Hist. of Mankind, vol. i. p. 51. Malte-Brun, vol. i. p. 507. Ibid. |