Page:The Zoologist, 4th series, vol 1 (1897).djvu/256

228 lives in the Mediterranean and on the African coast and islands and another in the West Indies. We can hardly believe that these creatures could easily traverse the whole Atlantic. The hypothesis of a former barrier of land between Africa and America, which we know is supported by other facts of distribution, would alone explain the difficulty.

On the other hand, in the Pacific we find no such break between the north and south. The aquatic mammals of Notopelagia have evidently had free access to the whole Pacific for a long period and have well availed themselves of this facility.

Again, while the great Southern Ocean exhibits a considerable uniformity of marine mammalian life, we see the Northern waters divided into two distinctly recognizable regions by the interposed masses of land. All these facts, with the one exception of the supposed Atlantic Barrier, would tend in favour of the now generally accepted doctrine that the principal masses of land and water are not of modern origin, but have existed mainly in their present shapes throughout all ages.

(1) — ''Halichœrus. Cystophora.—Hyperoodon. Delphinapterus. Monodon.''

(2) —''Monachus.—Manatus.—Inia. Pontoporia.''

(3) —Halicore.—Platanista.

(4) —''Otaria.—Rhytina. Rhachianectes.''

(5) —''Otaria. Macrorhinus.''

(6) —''Ogmorhinus. Lobodon. Leptonychotes. Ommatophoca. Otaria.—Neobalæna. Berardius.''