Since this was written, M. Alcide d'Orbingy has examined these shells, and pronounces them all to be recent.
 M. Aug. Bravard has described, in a Spanish work ('Observaciones Geologicas,' 1857), this district, and he believes that the bones of the extinct mammals were washed out of the underlying Pampean deposit, and subsequently became embedded with the still existing shells; but I am not convinced by his remarks. M. Bravard believes that the whole enormous Pampean deposit is a sub-aerial formation, like sand-dunes: this seems to me to be an untenable doctrine.
 Principles of Geology, vol. iv. p. 40.
 This theory was first developed in the Zoology of the Voyage of the Beagle, and subsequently in Professor Owen's Memoir on Mylodon robustus.
 I mean this to exclude the total amount which may have been successively produced and consumed during a given period.
 Travels in the Interior of South Africa, vol. ii. p. 207
 The elephant which was killed at Exeter Change was estimated (being partly weighed) at five tons and a half. The elephant actress, as I was informed, weighed one ton less; so that we may take five as the average of a full-grown elephant. I was told at the Surry Gardens, that a hippopotamus which was sent to England cut up into pieces was estimated at three tons and a half; we will call it three. From these premises we may give three tons and a half to each of the five rhinoceroses; perhaps a ton to the giraffe, and half to the bos caffer as well as to the elan (a large ox weighs from 1200 to 1500 pounds). This will give an average (from the above estimates) of 2.7 of a ton for the ten largest herbivorous animals of Southern Africa. In South America, allowing 1200 pounds for the two tapirs together, 550 for the guanaco and vicuna, 500 for three deer, 300 for the capybara, peccari, and a monkey, we shall have an average of 250 pounds, which I believe is overstating the result. The ratio will therefore be as 6048 to 250, or 24 to 1, for the ten largest animals from the two continents.
 If we suppose the case of the discovery of a skeleton of a Greenland whale in a fossil state, not a single cetaceous animal being known to exist, what naturalist would have ventured conjecture on the possibility of a carcass so gigantic being supported on the minute crustacea and mollusca living in the frozen seas of the extreme North?
 See Zoological Remarks to Capt. Back's Expedition, by Dr. Richardson. He says, "The subsoil north of latitude 56 degs. is perpetually frozen, the thaw on the coast not penetrating above three feet, and at Bear Lake, in latitude 64 degs., not more than twenty inches. The frozen substratum does not of itself destroy vegetation, for forests flourish on the surface, at a distance from the coast."
 See Humboldt, Fragments Asiatiques, p. 386: Barton's Geography of Plants: and Malte Brun. In the latter work it is said that the limit of the growth of trees in Siberia may be drawn under the parallel of 70 degs.
 Sturt's Travels, vol. ii. p. 74.
 A Gucho assured me that he had once seen a snow-white or Albino variety, and that it was a most beautiful bird.
 Burchell's Travels, vol. i. p. 280.
 Azara, vol. iv. p. 173.
 Lichtenstein, however, asserts (Travels, vol. ii. p. 25) that the hens begin sitting when they have laid ten or twelve eggs; and that they continue laying, I presume, in another nest. This appears to me very improbable. He asserts that four or five hens associate for incubation with one cock, who sits only at night.
 When at the Rio Negro, we heard much of the indefatigable labours of this naturalist. M. Aleide d'Orbigny, during the years 1825 to 1833, traversed several large portions of South America, and has made a collection, and is now publishing the results on a scale of magnificence, which at once places himself in the list of American travellers second only to Humboldt.
 Account of the Abipones, A.D. 1749, vol. i. (English Translation) p. 314
 M. Bibron calls it T. crepitans.
 The cavities leading from the fleshy compartments of the extremity, were filled with a yellow pulpy matter, which, examined under a microscope, presented an extraordinary appearance. The mass consisted of rounded, semi-transparent, irregular grains, aggregated together into particles of various sizes. All such particles, and the separate grains, possessed the power of rapid movement; generally revolving around different axes, but sometimes progressive. The movement was visible with a very weak power, but even with the highest its cause could not be perceived. It was very different from the circulation of the fluid in the elastic bag, containing the thin extremity of the axis. On other occasions, when dissecting small marine animals beneath the microscope, I have seen particles of pulpy matter, some of large size, as soon as they were disengaged, commence revolving. I have imagined, I know not with how much truth, that this granulo-pulpy matter was in process of being converted into ova. Certainly in this zoophyte such appeared to be the case.
 Kerr's Collection of Voyages, vol. viii. p. 119.
 Purchas's Collection of Voyages. I believe the date was really 1537.
 Azara has even doubted whether the Pampas Indians ever used bows.