which lives a wealth of animal life, including medusoids, small crustaceans, and especially "winged" gastropods (Clio). There are such quantities of these diatoms that their siliceous skeletons, which are of a most indestructible character, form a great ring of deposit known as diatom ooze at the bottom of the deep southern ocean, all round the South Polar Regions. Deep-sea deposits will be considered in due course, but at present I wish to call attention to a remarkable fact, namely, that the distribution of the diatoms on the surface is different from their distribution on the bottom. The maximum occurrence of diatoms in the surface waters is south of 60° S., whereas the maximum occurrence of diatoms at the bottom is in about 51° and 52° S. This is doubtless due to strong undercurrents running in a northerly direction, which carry the delicate skeletons northwards as they sink downwards towards the depths. This rain of diatom ooze must form food for minute forms of animal life, which in their turn fall a prey to larger animals living in intermediate and great depths.
The diatoms of the Polar Regions, however, are not all marine forms. I have examined hundreds of land forms in the Arctic Regions, especially during my wintering in 1896 and 1897 in Franz Josef Land. Doubtless, also, there are species of diatoms that belong to
