200. Further illustrations of alcyonarian spicules: _Eunicea_ (Studer) . . . 424 201–3. Associated, aggregated and composite calcospherites (Harting) . . . 425, 6 204. Harting’s “conostats” . . . 427 205. Liesegang’s rings (Leduc) . . . 428 206. Relay-crystals of common salt (Bowman) . . . 429 207. Wheel-like crystals in a colloid medium (_do._) . . . 429 208. A concentrically striated calcospherite or spherocrystal (Harting) . . . 432 209. Otoliths of plaice, shewing “age-rings” (Wallace) . . . 432 210. Spicules, or calcospherites, of _Astrosclera_ (Lister) . . . 436 211. 2. C- and S-shaped spicules of sponges and holothurians (Sollas and Théel) . . . 442 213. An amphidisc of _Hyalonema_ . . . 442 214–7. Spicules of calcareous, tetractinellid and hexactinellid sponges, and of various holothurians (Haeckel, Schultze, Sollas and Théel) . . . 445–452 218. Diagram of a solid body confined by surface-energy to a liquid boundary-film . . . 460 219. _Astrorhiza limicola_ and _arenaria_ (Brady) . . . 464 220. A nuclear “_reticulum plasmatique_” (Carnoy) . . . 468 221. A spherical radiolarian, _Aulonia hexagona_ (Haeckel) . . . 469 222. _Actinomma arcadophorum_ (_do._) . . . 469 223. _Ethmosphaera conosiphonia_ (_do._) . . . 470 224. Portions of shells of _Cenosphaera favosa_ and _vesparia_ (_do._) . . . 470 225. _Aulastrum triceros_ (_do._) . . . 471 226. Part of the skeleton of _Cannorhaphis_ (_do._) . . . 472 227. A Nassellarian skeleton, _Callimitra carolotae_ (_do._) . . . 472 228, 9. Portions of _Dictyocha stapedia_ (_do._) . . . 474 230. Diagram to illustrate the conformation of _Callimitra_ . . . 476 231. Skeletons of various radiolarians (Haeckel) . . . 479 232. Diagrammatic structure of the skeleton of _Dorataspis_ (_do._) . . . 481 233, 4. _Phatnaspis cristata_ (Haeckel), and a diagram of the same . . . 483 235. _Phractaspis prototypus_ (Haeckel) . . . 484 236. Annular and spiral thickenings in the walls of plant-cells . . . 488 237. A radiograph of the shell of _Nautilus_ (Green and Gardiner) . . . 494 238. A spiral foraminifer, _Globigerina_ (Brady) . . . 495 239–42. Diagrams to illustrate the development or growth of a logarithmic spiral . . . 407–501 243. A helicoid and a scorpioid cyme . . . 502 244. An Archimedean spiral . . . 503 245–7. More diagrams of the development of a logarithmic spiral . . . 505, 6 248–57. Various diagrams illustrating the mathematical theory of gnomons . . . 508–13 258. A shell of _Haliotis_, to shew how each increment of the shell constitutes a gnomon to the preexisting structure . . . 514 259, 60. Spiral foraminifera, _Pulvinulina_ and _Cristellaria_, to illustrate the same principle . . . 514, 5 261. Another diagram of a logarithmic spiral . . . 517 262. A diagram of the logarithmic spiral of _Nautilus_ (Moseley) . . . 519 263, 4. Opercula of _Turbo_ and of _Nerita_ (Moseley) . . . 521, 2