2. One of the Abdominal Somites of the Lobster, with its Appendages, separated and viewed from in Front 9 3. Third Maxilliped of Lobster 11 4. Walking Legs of Lobster 12 5. Appendages of Lobster in Front of Third Maxilliped 13 6. Dissection of Male Lobster, from the Side 16 7. Gills of the Lobster, exposed by cutting away the Side-flap of the Carapace (Branchiostegite) 18 8. First Larval Stage of the Common Lobster. × 4 28 9. Side-view of Rostrum of (A) Common Lobster (Homarus gammarus) and (B) American Lobster (Homarus americanus) 32 10. The "Fairy Shrimp" (Chirocephalus diaphanus), Male. × 2 35 11. Estheria obliqua, One of the Conchostraca 36 12. Daphnia pulex, a Common Species of "Water-flea." Much enlarged 37 13. Shells of Ostracoda. Much enlarged 38 14. Cyclops albidus, a Species of Copepod found in Fresh Water 39 15. Nebalia bipes. Enlarged 44 16. Mysis relicta, One of the Mysidacea. Enlarged 47 17. Gnathophausia willemoesii, One of the Deep-sea Mysidacea. Half Natural Size 48 18. Diastylis goodsiri, One of the Cumacea. Enlarged 49 19. Apseudes spinosus, One of the Tanaidacea. Enlarged 50 20. A Woodlouse (Porcellio scaber), One of the Isopoda. Enlarged 51 21. An Amphipod (Gammarus locusta). Enlarged 53 22. Two Species of Caprellidæ 54 23. Paracyamus boopis, the Whale-louse of the Humpback Whale 55 24. Meganyctiphanes norvegica, One of the Euphausiacea. Twice Natural Size 56 25. Larval Stages of the Common Shore Crab (Carcinus mænas—see Plate IX.) 68 26. Last Larval Stage of the Common Porcelain Crab (Porcellana longicornis—see