166, 7. Eggs segmenting under pressure: of Echinus and Nereis (Driesch), and of a frog (Roux) . . . 378

168. Various arrangements of a group of eight cells on the surface of a frog’s egg (Rauber) . . . 381

169. Diagram of the partitions and interfacial contacts in a system of eight cells . . . 383

170. Various modes of aggregation of eight oil-drops (Roux) . . . 384

171. Forms, or species, of Asterolampra (Greville) . . . 386

172. Diagrammatic section of an alcyonarian polype . . . 387

173, 4. Sections of Heterophyllia (Nicholson and Martin Duncan) . . . 388, 9

175. Diagrammatic section of a ctenophore (Eucharis) . . . 391

176, 7. Diagrams of the construction of a Pluteus larva . . . 392, 3

178, 9. Diagrams of the development of stomata, in Sedum and in the hyacinth . . . 394

180. Various spores and pollen-grains (Berthold and others) . . . 396

181. Spore of Anthoceros (Campbell) . . . 397

182, 4, 9. Diagrammatic modes of division of a cell under certain conditions of asymmetry . . . 400–5

183. Development of the embryo of Sphagnum (Campbell) . . . 402

185. The gemma of a moss (do.) . . . 403

186. The antheridium of Riccia (do.) . . . 404

187. Section of growing shoot of Selaginella, diagrammatic . . . 404

188. An embryo of Jungermannia (Kienitz-Gerloff) . . . 404

190. Development of the sporangium of Osmunda (Bower) . . . 406

191. Embryos of Phascum and of Adiantum (Kienitz-Gerloff) . . . 408

192. A section of Girardia (Goebel) . . . 408

193. An antheridium of Pteris (Strasburger) . . . 409

194. Spicules of Siphonogorgia and Anthogorgia (Studer) . . . 413

195–7. Calcospherites, deposited in white of egg (Harting) . . . 421, 2

198. Sections of the shell of Mya (Carpenter) . . . 422

199. Concretions, or spicules, artificially deposited in cartilage (Harting) . . . 423

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

265. A section of the shell of Melo ethiopicus . . . 525

266. Shells of Harpa and Dolium, to illustrate generating curves and gene . . . 526

267. D’Orbigny’s Helicometer . . . 529

268. Section of a nautiloid shell, to shew the “protoconch” . . . 531

269–73. Diagrams of logarithmic spirals, of various angles . . . 532–5

274, 6, 7. Constructions for determining the angle of a logarithmic spiral . . . 537, 8

275. An ammonite, to shew its corrugated surface pattern . . . 537

278–80. Illustrations of the “angle of retardation” . . . 542–4

281. A shell of Macroscaphites, to shew change of curvature . . . 550

282. Construction for determining the length of the coiled spire . . . 551

283. Section of the shell of Triton corrugatus (Woodward) . . . 554

284. Lamellaria perspicua and Sigaretus haliotoides (do.) . . . 555

285, 6. Sections of the shells of Terebra maculata and Trochus niloticus . . . 559, 60

287–9. Diagrams illustrating the lines of growth on a lamellibranch shell . . . 563–5

290. Caprinella adversa (Woodward) . . . 567

291. Section of the shell of Productus (Woods) . . . 567

292. The “skeletal loop” of Terebratula (do.) . . . 568

293, 4. The spiral arms of Spirifer and of Atrypa (do.) . . . 569

295–7. Shells of Cleodora, Hyalaea and other pteropods (Boas) . . . 570, 1

298, 9. Coordinate diagrams of the shell-outline in certain pteropods . . . 572, 3

300. Development of the shell of Hyalaea tridentata (Tesch) . . . 573

301. Pteropod shells, of Cleodora and Hyalaea, viewed from the side (Boas) . . . 575

302, 3. Diagrams of septa in a conical shell . . . 579

304. A section of Nautilus, shewing the logarithmic spirals of the septa to which the shell-spiral is the evolute . . . 581

305. Cast of the interior of the shell of Nautilus, to shew the contours of the septa at their junction with the shell-wall . . . 582

306. Ammonites Sowerbyi, to shew septal outlines (Zittel, after Steinmann and Döderlein) . . . 584

307. Suture-line of Pinacoceras (Zittel, after Hauer) . . . 584

308. Shells of Hastigerina, to shew the “mouth” (Brady) . . . 588

309. Nummulina antiquior (V. von Möller) . . . 591

310. Cornuspira foliacea and Operculina complanata (Brady) . . . 594

311. Miliolina pulchella and linnaeana (Brady) . . . 596

312, 3. Cyclammina cancellata (do.), and diagrammatic figure of the same . . . 596, 7

314. Orbulina universa (Brady) . . . 598

315. Cristellaria reniformis (do.) . . . 600

316. Discorbina bertheloti (do.) . . . 603

317. Textularia trochus and concava (do.) . . . 604

318. Diagrammatic figure of a ram’s horns (Sir V. Brooke) . . . 615

319. Head of an Arabian wild goat (Sclater) . . . 616

320. Head of Ovis Ammon, shewing St Venant’s curves . . . 621

321. St Venant’s diagram of a triangular prism under torsion (Thomson and Tait) . . . 623

322. Diagram of the same phenomenon in a ram’s horn . . . 623

323. Antlers of a Swedish elk (Lönnberg) . . . 629

324. Head and antlers of Cervus duvauceli (Lydekker) . . . 630

325, 6. Diagrams of spiral phyllotaxis (P. G. Tait) . . . 644, 5

327. Further diagrams of phyllotaxis, to shew how various spiral appearances may arise out of one and the same angular leaf-divergence . . . 648

328. Diagrammatic outlines of various sea-urchins . . . 664

329, 30. Diagrams of the angle of branching in blood-vessels (Hess) . . . 667, 8

331, 2. Diagrams illustrating the flexure of a beam . . . 674, 8

333. An example of the mode of arrangement of bast-fibres in a plant-stem (Schwendener) . . . 680

334. Section of the head of a femur, to shew its trabecular structure (Schäfer, after Robinson) . . . 681

335. Comparative diagrams of a crane-head and the head of a femur (Culmann and H. Meyer) . . . 682

336. Diagram of stress-lines in the human foot (Sir D. MacAlister, after H. Meyer) . . . 684

337. Trabecular structure of the os calcis (do.) . . . 685

338. Diagram of shearing-stress in a loaded pillar . . . 686

339. Diagrams of tied arch, and bowstring girder (Fidler) . . . 693

340, 1. Diagrams of a bridge: shewing proposed span, the corresponding stress-diagram and reciprocal plan of construction (do.) . . . 696

342. A loaded bracket and its reciprocal construction-diagram (Culmann) . . . 697

343, 4. A cantilever bridge, with its reciprocal diagrams (Fidler) . . . 698

345. A two-armed cantilever of the Forth Bridge (do.) . . . 700

346. A two-armed cantilever with load distributed over two pier-heads, as in the quadrupedal skeleton . . . 700

347–9. Stress-diagrams. or diagrams of bending moments, in the backbones of the horse, of a Dinosaur, and of Titanotherium . . . 701–4