A. The greater abundance of Radiolaria in the tropical seas is probably to be explained by the more favourable conditions of existence, and in particular the larger quantity of nutritive material (especially of decayed animals) and not by the higher temperature of the surface, for at depths of from 2000 to 3000 fathoms where the abyssal Radiolaria live, the temperature is but little above the freezing point or even below it (compare the bottom temperatures in the list of Challenger Stations, § 240). B. Station 271 of the Challenger Expedition, situated almost on the equator in the Mid Pacific (lat. 0° 33' S.), exceeds all other parts of the earth, hitherto known, in respect of its wealth in Radiolaria, and this is true of the pelagic as well as of the zonarial and abyssal forms. In the Station List the deposit at this point is stated to be "Globigerina ooze"; but after the calcareous matter has been removed by means of acid, the purest Radiolarian ooze remains, rich in varied and remarkable species. More than one hundred new species have been described from this Station alone. C. Regarding the Arctic Radiolaria compare the contributions of Ehrenberg (L. N. 24, pp. 138, 139, 195) and Brady on the English North Polar Expedition, 1875-76 (Ann. and Mag. Nat. Hist., 1878, vol. i. pp. 425, 437). D. Regarding the Antarctic Radiolaria, compare § 230, note A, and Ehrenberg, Mikrogeologie (L. N. 6, Taf. xxxv., A.), also L. N. 24, pp. 136-139.