Such is the number of the known vertebrates, exclusive of the fishes, with which in this question we have now to deal. Still, however, there are a few lingering theologians, some of them very intelligent men, who continue to regard the ark as quite big enough for them all. Dr. Hamilton of Mobile, for instance, after fairly stating Swainson's estimate, namely, one thousand mammalia, six thousand birds, and one thousand five hundred reptiles and amphibiæ, goes on to say, that "it must not be forgotten, that of all these, the vastly greater proportion are small; and that numbers of them could be placed together in the same compartment of the ark." This, however, permit me to say with all respect, is not meeting the real difficulty. No doubt many of the birds are small,--many of the reptiles are small,--many even of the mammals are small,--many small animals were known in the days of Raleigh, and a much greater number of small animals are known now; but the question proper to the case seems to be, What proportions do both the large and the small animals now known bear to the large and small animals known in the days of Raleigh or Buffon; and how much additional accommodation-room would they require during their supposed voyage of a twelvemonth? There are two different ways in which the list of the known animals has been increased, especially of the known mammals. They have been increased in a certain appreciable proportion by _discovery_; and as discovery has been made chiefly in islands,--for the great continents had been previously known,--and as the mammals of islands, as has been well remarked by Cuvier, are usually small, of this appreciable proportion the bulk is comparatively not great. The great kangaroo (_Macropus giganteus_), though the inhabitant of an island which ranks among the continents, would not much exceed in bulk, tried by Raleigh's quaint scale of measurement, a sheep and a half, or at most two sheep; and yet I know not that discovery in the islands has added a larger animal to the previously known ones than the great kangaroo. Mr. Waterhouse, when he published, in 1841, his "History of the Marsupialia," reckoned up one hundred and five distinct species of pouched animals; and eighteen species more,--in all one hundred and twenty-three,--have been since added to the order. With the exception of an opossum or two, all these marsupiata may be regarded as discoveries made since the time of Buffon; most of them, as I have said, are small. And such, generally, has been the nature of the revelations made during the last seventy years by positive _discovery_. It is not, however, by discovery, but by scientific scrutiny into the true nature and distinctions of species, that the recent enormous increase in the number of the known mammals has mainly taken place. And in these cases it will generally be found that the new species, which had been previously confounded with some old ones, so nearly resemble the latter in bulk, as