1. _Sphagnum acutifolium_, expanded leaf. 2. _Sphagnum acutifolium_, cells of leaf. 3. Spermatozoa of _Polytrichum piliferum_. 4. _Sphagnum acutifolium._ 5. _Sphagnum acutifolium_, capsule. 6. _Gymnostomum truncatulum._ 7. _Gymnostomum truncatulum_, leaf. 8. _Gymnostomum truncatulum_, capsule and operculum. 9. _Gymnostomum truncatulum_, spore. 10. _Dicranum heteromallum._ 11. _Dicranum heteromallum._ 12. _Dicranum heteromallum_, leaf. 13. _Dicranum heteromallum_, operculum. 14. _Dicranum heteromallum_, calyptra. 15. _Dicranum heteromallum_, capsule; 15 _a_, peristome. 16. _Tortula muralis._ 17. _Tortula muralis_, leaf. 18. _Tortula muralis_, capsule; _a_, tooth of peristome. 19. _Tortula muralis_, operculum. 20. _Tortula muralis_, calyptra. 21. _Tortula muralis_, archegonia. 22. _Polytrichum piliferum._ 23. _Polytrichum piliferum_, leaf. 24. _Polytrichum piliferum_, calyptra. 25. _Polytrichum piliferum_, antheridial stems. 26. _Polytrichum piliferum_, single head. 27. _Polytrichum piliferum_, antheridia and paraphyses. 28. _Funaria hygrometrica._ 29. _Funaria hygrometrica._ 30. _Funaria hygrometrica_, leaf. 31. _Funaria hygrometrica_, capsule; _a_, operculum. 32. _Funaria hygrometrica_, stalk-like body. 33. _Funaria hygrometrica_, young archegone. 34. _Funaria hygrometrica_, more advanced archegone. 35. _Funaria hygrometrica_, section of young capsule. 36. _Funaria hygrometrica_, calyptra. 37. _Funaria hygrometrica_, antheridia. 38. _Funaria hygrometrica_, spores. 39. _Funaria hygrometrica_, annulus. 40. _Funaria hygrometrica_, archegonia. 41. _Funaria hygrometrica_, antheridial head. 42. _Funaria hygrometrica_, peristome. 43. _Hypnum rutabulum._ 44. _Hypnum rutabulum_, leaf. 45. _Hypnum rutabulum_, capsule. 46. _Hypnum rutabulum_, spores. 47. _Hypnum rutabulum_, peristome. 48. _Hypnum rutabulum_, cells of leaf. 49. _Bryum capillare._ [Illustration: Plate III. W Bagg sculp _London: John Van Voorst._] The calyptra is either simply mitre-shaped, or _mítriform_ (Pl. III. fig. 24), or it is half-cleft, or _dimid´iate_ (figs. 14, 36). When the capsule is ripe, the upper part usually separates at a circular horizontal line (fig. 8) as a kind of lid, which is called the _oper´culum_ (_operculum_, a lid), and thus the spores are enabled to escape. The rim of the capsule, from which the operculum has separated, forms its mouth, and this often exhibits a fringe of teeth (figs. 15, 18, 31), arranged in one or more rows; sometimes the teeth are replaced by a membrane, or, again, both teeth and a membrane may be present. This mouth-fringe is the _per´istome_ (περἰ, around, στὁμα, mouth). In many mosses, an elastic row or ring of cells is situated between the mouth of the capsule and its operculum, called the _annulus_ (figs. 18 & 39); this, when the capsule is ripe, aids in throwing off the operculum.