Thus Dr.{149} Guenther has described[156] a frog from Chile by the name of cacotus, which singularly resembles the European bombinator.
[Illustration: SOLENODON.] Again of the salmons, two genera from South America, New Zealand, and Australia, are analogous to European salmons.
In addition to this may be mentioned a quotation from Professor Dana, given by Mr.Darwin,[157] to the effect that "it is certainly a wonderful fact that New Zealand should have a closer resemblance in its crustacea to Great Britain, its antipode, than to any other part of the world:" and Mr.Darwin adds "Sir J.Richardson also speaks of the reappearance on the shores of New Zealand, Tasmania, &c.

of northern forms of fish.

Dr.Hooker informs me that twenty-five species of algae are common to New Zealand and to {150} Europe, but have not been found in the intermediate tropical seas." Many more examples of the kind could easily be brought, but these must suffice.

As to the last-mentioned cases Mr.Darwin explains them by the influence of the glacial epoch, which he would extend actually across the equator, and thus account, amongst other things, for the appearance in Chile of frogs having close genetic relations with European forms.

But it is difficult to understand the persistence and preservation of such exceptional forms with the extirpation of all the others which probably accompanied them, if so great a migration of northern kinds had been occasioned by the glacial epoch.
Mr.Darwin candidly says,[158] "I am far from supposing that all difficulties in regard to the distribution and affinities of the identical and allied species, which now live so widely separated in the north and south, and sometimes on the intermediate mountain-ranges, are removed." ...
"We cannot say why certain species and not others have migrated; why certain species have been modified and have given rise to new forms, whilst others have remained unaltered." Again he adds, "Various difficulties also remain to be solved; for instance, the occurrence, as shown by Dr.Hooker, of the same plants at points so enormously remote as Kerguelen Land, New Zealand, and Fuegia; but icebergs, as suggested by Lyell, may have been concerned in their dispersal.