“The individuals of genera, on continents, spread and widely diffuse themselves, and by the difference of localities, nourishment, and soil, form varieties; and being in consequence of their isolation never crossed by other varieties, and so brought back to the main type, they in the end become a permanent and a distinct species. Then, perhaps, in other ways, they once more become associated with other descendants of the original form—which have likewise become new varieties—and both now appear as very distinct species, no longer mingling with one another. Not so on islands. Being commonly confined in narrow valleys or within the limit of small zones, individuals can reach one another and destroy every commencing production of a permanent variety. Much in the same way the peculiarities or faults in language, originating with the head of some family, become, through the extension of the family, indigenous throughout a whole district. If the district is separated and isolated, and if the language is not brought back to its former purity by constant connection with that spoken in neighbouring districts, a dialect will be the result. If natural obstacles, forests, constitution, form of government, unite the inhabitants of the separate district still more closely, and separate them still more completely from their neighbours, the dialect is fixed, and becomes a completely distinct language.” (Uebersicht der Flora auf den Canarien, S. 133.) We perceive that Buch is here led to the fundamental idea of the Theory of Descent by the phenomena of the geography of plants, a department of biological knowledge which in fact furnishes a mass of proofs in favour of it. Darwin has minutely discussed these proofs in two separate chapters of his book (the 11th and 12th). Buch’s remark is further of interest, because it leads us to the exceedingly instructive comparison of the different branches of language with the species of organisms, a comparison which is of the greatest use to Comparative Philology, as well as to Comparative Botany and Zoology. Just as, for example, the different dialects, provincialisms, branches, and off-shoots of the German, Slavonic, Greco-Latin, and Irano-Indian parent language, are derived from a single common Indo-Germanic parent tongue, and just as their _differences_ are explained by _Adaptation_, and their common _fundamental characters_ explained by _Inheritance_, so in like manner the different species, genera, families, orders, and classes of Vertebrate animals are derived from a single common vertebrate form of animal. Here also Adaptation is the cause of differences, Inheritance the cause of community of character. This interesting parallelism in the divergent development of the forms of speech and the forms of organisms has been discussed in the clearest manner by one of our first comparative philologists, the talented Augustus Schleicher, whose premature death, four years ago, remains an irreparable loss, not only