THERE have been few more enduring puzzles in natural history than the nature of the Coccoliths, described by the late Mr. Huxley from Captain Dayman's deep-sea soundings in the North Atlantic in H.M.S. Cyclops in the summer of 1857. Dr. G. C. Wallich, who was on board H.M.S. Bulldog, engaged in a preparatory survey of the route for a telegraph cable about the same date, observed the aggregation of the Coccoliths into spheres, to which he gave the name of Coccospheres. He also pointed out the identity of the Coccoliths with bodies observed in chalk by Mr. Sorby. Mr. Huxley associated them with that unfortunate organism Bathy-bins. “I am led to believe that they are not independent organisms, but that they stand in the same relation to the protoplasm of Bathybius as the spicula of Sponges or of Radiolaria do to the soft part of those animals” (Qztarl. Journ. Micr. Sci., vol. viii. N.S.p. 210, 1868). Prof. Haeckel, who received some ooze dredged by Wyville Thomson and Carpenter (Porcupine Exped.), put a like interpretation on the phenomena, and published in the Jenaische Zeitschrift, vol. v., 1870, a detailed account of the matter with illustrations. Bathybius is dead, but one cannot leave it without the reflection that there are few naturalists, the young and expert included, but would have given similar explanation of the appearances. The Challenger Expedition next entered the field, and discovered Coccospheres and Rhabdospheres on the surface of the ocean, living free in the water, entangled in the protoplasmic matter of Foraminifera and Radiolaria, and in the stomachs of Crustacea and Salpæ. The Rhabdospheres are known only from the tropics, and the Coccospheres, though tropical as well, yet find their finest development in temperate seas. “There is considerable variety both in the form and size of Coccospheres and Rhabdospheres, some varieties having the component parts (Coccoliths and Rhabdoliths) much more compactly united into a sphere than others. The interior of the spheres is perfectly clear when examined fresh from the surface, and becomes coloured brown with iodine solution, but with iodine and sulphuric acid no blue colour was observed. They were never observed to colour with carmine solution. When the calcareous parts are removed by dilute acids, a small gelatinous sphere remains, in the outer layer of which the Coccoliths and Rhabdoliths were embedded” (Challenger Reports, “Narrative,” vol. i. p. 939). In the Report on the Deep-Sea Deposits, Dr. John Murray treats them as pelagic calcareous algæ (p. 257), and one of us has been criticised with some severity for adopting this view in an “Introduction to the Study of Seaweeds.” The Hensen Plankton Expedition, probably through using silk nets of too coarse a texture, failed altogether to find Coccospheres or Rhabdospheres, and Dr. Schütt, the botanist of that expedition (“Pflanzenleben der Hochsee,” p. 44), casts doubt on their very existence as organisms, and in any case will have none of them in the vegetable kingdom. Many other naturalists, wise and eminent, British and foreign, have shared, and do share, the opinion of Schütt.