The few paragraphs in which Peron expressed his views regarding the modification of species may be quoted. It has to be remembered that they were written in the early years of the nineteenth century, when ideas on this subject were in a state of uncertainty rather than of transition, and more than half a century before Darwin gave an entirely new direction to thought by publishing his great hypothesis. Cuvier at this time believed in the fixity of species--constancy in the type with modification in the form of individuals; but his opinions underwent some amount of change in the latter part of his career. The point argued with such gravity, and the conclusion which Peron stresses with the impressiveness of italics, are not such as a naturalist nowadays would think it worth while to elaborate, namely, that organisms having a general structural similarity are modified by climate and environment. It would not require a voyage to another hemisphere to convince a schoolboy of that truth nowadays. But the paragraphs have a certain historical value, for they put what was evidently an important idea to an accomplished naturalist a century ago. They present us, in that aspect, with an interesting bit of pre-Darwinian generalisation. "Before natural history had acquired a strict and appropriate language of its own," wrote Peron,* (* Voyage de Decouvertes, 1824 edition 3 243.) "when its methods were defective and incomplete, travellers and naturalists confused under one name, in imitation of each other, so to speak, animals which were essentially different. There is no class of the animal kingdom which, in the actual state of things, does not include several orbicular species; that is to say, several species which are in some degree common to all parts of the globe, however they may be modified by geographical and climatic conditions. Other species, although confined to certain latitudes, are, however, usually regarded as common to all climates, and to all seas comprised within these latitudes. The existence of these last animals is regarded as being independent of latitude. To confine ourselves to marine species, one sees it constantly repeated in books of the most estimable character, that the great whale (Balaena mysticetus, Linn.) is found equally amidst the frozen waters of Spitzbergen and in the Antarctic seas; that the sharks and seals of various kinds are found in equally innumerable tribes in seas the farthest apart in the two hemispheres; that the turtle and the tortoise inhabit indifferently the Atlantic, the Indian, and the great equinoctial oceans.