of various species, some of which alighted on the ship, while others were thrown with violence against the sails. In this manner islands become tenanted by species of birds inhabiting the nearest main land. Geographical Distribution and Dissemination of Reptiles. A few facts respecting the third great class of vertebrated animals, will suffice to show that the plan of nature, in regard to their location on the globe, is perfectly analogous to that already exemplified in other parts of the organic creation, and has probably been determined by similar causes. Of the great saurians, the gavials which inhabit the Ganges differ from the cayman of America, or the crocodile of the Nile. The monitor of New Holland is specifically distinct from the Indian species; these latter again from the African, and all from their congeners in the new world. So in regard to snakes; we find the boa of America, represented by the python, a different though nearly allied genus, in India. America is the country of the rattle-snake, Africa of the cerastes, and Asia of the hooded snake or cobra di capello. There is a legend that St. Patrick expelled all reptiles from Ireland, and certain it is that none of the three species of snakes common in England, nor the toad, have been observed there by naturalists, They have our common frog, and our water-newt, and according to Ray (Quad. 264.) the green lizard (Lacerta viridis). Schultes the botanist observed, a few years since, in his tour in England, that there were two great islands in Europe of which the floras were unknown, Sardinia and Ireland; we believe he might also have added the fauna of the latter country. The range of the large reptiles is, in general, quite as limited as that of some orders of the terrestrial mammalia. The great saurians sometimes cross a considerable tract, in order to pass from one river to another; but their motions by land are generally slower than those of quadrupeds. By water, however, they may transport themselves to distant situations more easily. The larger alligator of the Ganges sometimes descends beyond the brackish water of the Delta into the sea, and in such cases * it might chance to be drifted away by a current, and survive till it reached a shore at some distance; but such casualties are probably very rare *. Turtles migrate in large droves from one part of the ocean to another during the ovipositing season. Dr. Fleming† mentions that an individual of the hawk's bill turtle (Chelonia imbricata) so common in the American seas has been taken at Papa Stour, one of the West Zetland islands; and according to Sibbald, "the same animal came into Orkney." Another was taken in 1774, in the Severn, according to Turton. Two instances also of the occurrence of the leathern tortoise (C. coriacea), on the coast of Cornwall, in 1756, are mentioned by Borlase. These animals of more southern seas can only be considered as stragglers attracted to our shores during uncommonly warm seasons by an abundant supply of food, or driven by storms to high latitudes. Some of the smaller reptiles lay their eggs on aquatic plants; and these must often be borne rapidly by rivers, and conveyed to distant regions, in a manner similar to the dispersion of seeds before adverted to. But that the larger ophidians may be themselves transported across the seas is evident from the following most interesting account of the arrival of one at the island of St. Vincent. It is worthy of being recorded, says the Rev. L. Guilding, "that a noble specimen of the Boa constrictor was lately conveyed to us by the currents, twisted round the trunk of a large sound cedar tree, which had probably been washed out of the bank by the floods of some great South American river, while its huge folds hung on the branches, as it waited for its prey. The monster was fortunately destroyed after killing a few sheep, and his skeleton now hangs before me in my study, putting me in mind how much reason I might have had to fear in my future rambles through the forests of St. Vincent, had this formidable reptile been a pregnant female, and escaped to a safe retreat.” *Malte-Brun says (Syst. of Geog. vol. viii. p. 193), that a crocodile is still preserved at Lyons that was taken from the Rhone, about two centuries ago; but no particulars are given. Brit. Animals, p. 149; who cites Sibbald. Zool. Journ. vol. iii. p. 406. Dec. 1827. CHAPTER VII. Geographical distribution and migrations of fish-of testacea-Causes which limit the extension of many species-Their mode of diffusion-Geographical range of zoophytes-Their powers of dissemination-Distribution of insectsMigratory 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 speciesProgress 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 which they brought to Europe from the southern 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 and medusæ to the cetacea. sponges 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 66 The fish of the Arabian gulf are said to differ entirely from *Sur les Habitations des Animaux Marins. Ann. du Mus. tom. xv., cited by Prichard, Phys. Hist. of Mankind, vol. i. p. 51. 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 crampfish, is said to be dispersed over all tropical and many temperate seast. 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 herring and the haddock, after frequenting certain shores in vast shoals for a series of years, desert them again and resort to other stations, followed by the species which prey on them. Eels are said to descend into the sea for the purpose of producing their young, which are seen returning into the freshwater by myriads, extremely small in size, but possessing the power of surmounting every obstacle which occurs in the course of a river, by applying their slimy and glutinous bodies to the surface of rocks, or the gates of a lock, even when dry, and so climbing over it ‡. Gmelin says, that the anseres subsist in their migrations on the spawn of fish, and that oftentimes when they void the spawn, two or three days afterwards, the eggs retain their vitality unimpaired §. When there are many disconnected freshwaterlakes in a mountainous region, at various elevations, each remote from the other, it has often been deemed inconceivable how they could all become stocked with fish from one common source; but it has been suggested, that the minute eggs of *Malte-Brun, vol.i. p. 507. Phil. Trans. 1747, p. 395. +Ibid. these animals may sometimes be entangled in the feathers of water-fowl. These, when they alight to wash and plume themselves in the water, may often unconsciously contribute to propagate swarms of fish, which, in due season, will supply them with food. Some of the water-beetles, also, as the dyticidæ, are amphibious, and in the evening quit their lakes and pools, and flying in the air transport the minute ova of fishes to distant waters. In this manner some naturalists account for the fry of fish appearing occasionally in small pools caused by heavy rains. Geographical Distribution and Migrations of Testacea. The testacea, of which so great a variety of species occurs in the sea, are a class of animals of peculiar importance to the geologist, because their remains are found in strata of all ages, and generally in a higher state of preservation than those of other organic beings. Climate has a decided influence on the geographical distribution of species in this class; but as there is much greater uniformity of temperature in the waters of the ocean, than in the atmosphere which invests, the land, the diffusion of many marine molluscs is extensive. Some forms, as those of the nautili, volutæ, and cyprææ, attain their fullest development in warm latitudes; and most of their species are exclusively confined to them. Péron and Lesueur remark, that the Haliotis gigantea, of Van Dieman's land, and the Phasianella, diminish in size as they follow the coasts of New Holland to King George's straits, and entirely disappear beyond them*. Almost all the species of South American shells differ from those of the Indian archipelago in the same latitudes; and on the shores of many of the isles of the South Pacific, peculiar species have been obtained. But we are as yet by no means able to sketch out the submarine provinces of shells, as the botanist has done those of the terrestrial, and even of the subaqueous plants. There can be little * Ann. du Mus. d'Hist. Nat., tom. xv, |