XX LIST OF ILLUSTRATIONS 



FIG. PAGK 



226. Silver fish {Lepisma saccharina), one of the Thysanura . 405 



227. Acerentomon, a very primitive insect .... 408 



228. Mosquito — after Nuttall and Shipley . . . .411 



229. Scorpion, ventral surface . . . . .413 



230. Scorpion, dorsal surface . . . • • -415 



231. Sex dimorphism in a spider (iVg/?/ii7a mgm) — after Vinson . 418 



232. Dissection of My gale from the ventral surface — after Cuvier . 419 



233. Section of lung-book — after Macleod .... 420 



234. Follicle-mite (greatly enlarged) .... 423 



235. Itch-mite {Sarcoptes scahiei) (greatly enlarged) . . 423 



236. Tick [Ixodes riduvius, female), dorsal surface (after Wheler), 



showing the oval shield ..... 424 



237. Tick {Ixodes riduvius, female), ventral surface — after 



Wheler ....... 424 



238. Mouth-parts of a tick ...... 425 



239. Limulus or King-crab, ventral aspect .... 427 



240. Limulus or King-crab, dorsal aspect .... 428 



241. Yowng Limulus — after Walcott. .... 429 



242. Trilobite (Conocephalites) — after Barrande . . . 430 



243. Vertical cross-section of a Trilobite (Calymene) — after 



Walcott . . . . • • -430 



244. Under-surface of a Trilobite — after Beecher . . -431 



245. Sea-spider {Pycnogonum littorale), from the dorsal surface . 432 



246. Male of Nymphon — after Sars ..... 432 



247. Ideal mollusc — after Ray Lankester .... 434 



248. Stages in molluscan development .... 435 



249. Roman snail (Helix pomatia) ..... 436 



250. Vertical section of the shell of a species of Helix . . 437 



251. Dissection of snail ...... 442 



252. Reproductive organs of Wg/j;t /jowa^za — after Meisenheimer . 443 



253. Snail (//e/jA;^owai!Ja) laying its eggs — after Meisenheimer . 444 



254. Diagram of larva of Paludina — after Erlanger . . 445 



255. The fresh-water mussel (C7mo) ..... 447 



256. Structure of Anodonta — after Rankin .... 45i 



257. Glochidium larva of the fresh-water mussel . . . 454 



258. Side view of Se^m — after Jatta .... 456 



259. External appearance of a squid {Loligo) . . . 458 



260. Diagram of the structure of Sepia — mainly after Pelseneer . 459 



261. Diagram of circulatory and excretory systems in a Decapod 



like Sepia — after Pelseneer .... 463 



262. Male of Argonauta (after Jatta), showing " hectocotylus " 



arm ; compare Fig. 9, showing the female . . 464 



