The address of T. Baldwin Spence, President of the Biological Section of the Australian Association, dealt with the fresh-water and terrestrial fauna of Tasmania, and the introduction of the present animals of Australia and the way their descendants had become distributed. The struthious birds—the ostriches, emus, cassowaries, and kiwis—were, with the exception of the African ostrich, which ranged into Arabia, confined to the southern hemisphere, while they were supposed to have originated in the northern hemisphere and migrated southward. But by this hypothesis there were great difficulties in explaining how the struthious birds reached Australia and New Zealand without being accompanied by placental mammals. Also, the struthious birds of New Zealand, including the lately extinct moas, were smaller, and made a nearer approach to the flying birds, from which the struthious birds were descended, than did any of the others, and they should expect to find the least altered forms near the place of origin. The tinamus of Central and South America, although flying birds, resembled the New Zealand struthious birds in several particulars; and as a former connection between New Zealand and South America was shown by the plants, the frogs, and the land shells, it seemed more probable that the struthious birds of Australasia originated in the neighborhood of New Zealand from flying birds related to the tinamus, and that they spread thence into Australia and New Guinea, rather than that they should have migrated southward from Asia. Probably the ostriches of Africa and South America have a different line of descent from the struthious birds of Australasia, and might have originated from swimming birds in the northern hemisphere.